Chemistry › Spectroscopy

Molecular Spectroscopy and Structure

Works Count: 48727

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This cluster of papers focuses on the use of rotational spectroscopy, particularly broadband microwave and Fourier transform techniques, to determine the molecular structures of various compounds in the gas phase. The studies explore topics such as hydrogen bonding, conformational dynamics, internal rotation, and torsional states of molecules.

Keywords

Rotational Spectroscopy; Molecular Structure; Broadband Microwave Spectroscopy; Gas Phase; Hydrogen Bonds; Conformational Dynamics; Chirped-Pulse Excitation; Fourier Transform Microwave Spectroscopy; Internal Rotation; Torsional States

Conformational analysis—CI

1974-01-01

David H. Wertz , Norman L. Allinger

Polarizability of the Hydrogen Molecule

1967-02-15

W. Kol os , L. Wolniewicz

A variation perturbation method has been employed to calculate the static dipole polarizabilities of the hydrogen molecule. The wavefunction was represented by an expansion in elliptic coordinates including the interelectronic … A variation perturbation method has been employed to calculate the static dipole polarizabilities of the hydrogen molecule. The wavefunction was represented by an expansion in elliptic coordinates including the interelectronic distance. A 54-term expansion was used for the zero-order wavefunction and 34 terms for the first-order corrections. The polarizabilities computed for several values of the internuclear distance (0.4≤R≤4.0) were averaged for various vibrational and rotational states of H2, HD, and D2. The results are in a satisfactory agreement with the experimental values.

Microwave molecular spectra

1972-02-01

Walter Gordy , Robert I. Cook

Vibration–Rotation Structure in Asymmetric- and Symmetric-Top Molecules

1972-01-01

I.M. Mills

Determination of Molecular Structures from Ground State Rotational Constants

1958-10-01

C. C. Costain

Kraitchman has shown that a single isotopic substitution on an atom is sufficient to determine directly the coordinates of that atom with respect to the principal axes of the original … Kraitchman has shown that a single isotopic substitution on an atom is sufficient to determine directly the coordinates of that atom with respect to the principal axes of the original molecule. Kraitchman's formulas represent exact solutions of the equations for the equilibrium moments of inertia. However, the effects of the zero-point vibrations are such that the coordinates obtained by substitution from the ground state moments of inertia I0 are systematically less than r0. These coordinates have here been called r (substitution) or rs, and it is found that rs≃(r0+re)/2, and Is= ∑ imirsi2≃(I0+Ie)/2. In the usual method of solution, the coordinate of one atom is determined from the equation for I0, and therefore the difference I0—Is must be made up by this one coordinate. This introduces a large error in the structures normally determined from ground state constants, and results in variations of 0.01 A in structures determined from different sets of isotopic species. If instead, we obtain the structure only from the rs coordinates and make no attempt to reproduce the I0 values, the structure is virtually independent of the isotopic species used in the determination. The variation in the structures obtained from different sets of isotopic species appears to depend only on the uncertainties in the rotational constants. In addition, the accuracy is independent of the mass of the substituted atom, and therefore H atoms are located just as accurately as the heavier atoms. The rs structures of HCN, N2O, OCS, CH3CCH, CH3CN, CH3NC, and the methyl halides have been determined by the isotopic substitution method. For the first three molecules comparisons can be made with equilibrium data, and it is found that the rs bond lengths are no more than 0.002 A greater than the re. The primary interest in the other molecules studied is in the structure of the methyl group. The anomalous separation of the H and D coordinates previously found is readily explained and does not appear in the rs structures. The consistency of the results is such that comparisons between molecules can be made with confidence.

Internal Rotation and Microwave Spectroscopy

1959-10-01

Chun C. Lin , J. D. Swalen

Gauche effect. Stereochemical consequences of adjacent electron pairs and polar bonds

1972-03-01

Saul Wolfe

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGauche effect. Stereochemical consequences of adjacent electron pairs and polar bondsSaul WolfeCite this: Acc. Chem. Res. 1972, 5, 3, 102–111Publication Date (Print):March 1, 1972Publication History Published online1 … ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGauche effect. Stereochemical consequences of adjacent electron pairs and polar bondsSaul WolfeCite this: Acc. Chem. Res. 1972, 5, 3, 102–111Publication Date (Print):March 1, 1972Publication History Published online1 May 2002Published inissue 1 March 1972https://pubs.acs.org/doi/10.1021/ar50051a003https://doi.org/10.1021/ar50051a003research-articleACS PublicationsRequest reuse permissionsArticle Views1852Altmetric-Citations732LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Normal Vibrations of N-Methylacetamide

1958-09-01

Tatsuo Miyazawa , Takehiko Shimanouchi , San-ichiro Mizushima

The in-plane normal vibrations of N-methylacetamide and its deuterated compound were calculated as a six-body problem. The force constants were transferred from diformylhydrazine and other molecules with similar structures. The … The in-plane normal vibrations of N-methylacetamide and its deuterated compound were calculated as a six-body problem. The force constants were transferred from diformylhydrazine and other molecules with similar structures. The normal modes as well as the distributions of the potential energy among symmetry coordinates were also calculated. The result of these calculations allows quantitative discussions concerning the nature of the amide I, II, II′, III, III′, and IV vibrations and other normal vibrations of N-methylacetamide.

Molecular Orbital Studies of Hydrogen Bonds. III. C=O···H–O Hydrogen Bond in H2CO···H2O and H2CO···2H2O

1971-08-01

Keiji Morokuma

Ab initio LCAO–MO–SCF calculation for H2CO···H2O is carried out with a minimal Slater basis set. The most stable conformation has an O···H distance of 1.89 Å with <C=O···H=− 64° and … Ab initio LCAO–MO–SCF calculation for H2CO···H2O is carried out with a minimal Slater basis set. The most stable conformation has an O···H distance of 1.89 Å with <C=O···H=− 64° and a stabilization energy of 3.5 kcal/mole, about a half of that for H2O···H2O. Nonlinear and π hydrogen bonds, H2CO···2H2O and the O···H–C hydrogen bond in H2O···HCHO, are also studied. An energy decomposition scheme is proposed and applied to H2CO···H2O and H2O···H2O. In the latter the electrostatic energy 8.0 kcal/mole, the exchange repulsion − 9.9 kcal/mole, the polarization and dispersion energy 0.3 kcal/mole, and the delocalization energy 8.2 kcal/mole are in good agreement with Coulson's estimates.

An Extended Hückel Theory. I. Hydrocarbons

1963-09-15

Roald Hoffmann

The Hückel theory, with an extended basis set consisting of 2s and 2p carbon and 1s hydrogen orbitals, with inclusion of overlap and all interactions, yields a good qualitative solution … The Hückel theory, with an extended basis set consisting of 2s and 2p carbon and 1s hydrogen orbitals, with inclusion of overlap and all interactions, yields a good qualitative solution of most hydrocarbon conformational problems. Calculations have been performed within the same parametrization for nearly all simple saturated and unsaturated compounds, testing a variety of geometries for each. Barriers to internal rotation, ring conformations, and geometrical isomerism are among the topics treated. Consistent σ and π charge distributions and overlap populations are obtained for aromatics and their relative roles discussed. For alkanes and alkenes charge distributions are also presented. Failures include overemphasis on steric factors, which leads to some incorrect isomerization energies; also the failure to predict strain energies. It is stressed that the geometry of a molecule appears to be its most predictable quality.

The structure of water dimer from molecular beam electric resonance spectroscopy

1977-01-15

T. R. Dyke , Kenneth M. Mack , J. S. Muenter

Molecular beams of hydrogen bonded water dimer, generated in a supersonic nozzle, have been studied using electric resonance spectroscopy. Radiofrequency and microwave transitions have been observed in (H2 16O)2, (D2 … Molecular beams of hydrogen bonded water dimer, generated in a supersonic nozzle, have been studied using electric resonance spectroscopy. Radiofrequency and microwave transitions have been observed in (H2 16O)2, (D2 16O)2, and (H2 18O)2. Transitions arising from both pure rotation and rotation–tunneling occur. The pure rotational transitions have been fit to a rigid rotor model to obtain structural information. Information on the relative orientation of the two monomer units is also contained in the electric dipole moment component along the A inertial axis μa, which is obtained from Stark effect measurements. The resultant structure is that of a ’’trans-linear’’ complex with an oxygen–oxygen distance ROO of 2.98(1) Å, the proton accepting water axis is 58(6) ° with respect to ROO, and the proton donating water axis at −51(6) ° with respect to ROO. This structure is consistent with a linear hydrogen bond and the proton acceptor tetrahedrally oriented to the hydrogen bond. The limits of uncertainty are wholly model dependent and are believed to cover variations from the zero-point vibrational structure observed to the equilibrium structure. μa shows strong dependence on J and K and is about 2.6 D. Centrifugal distortion constants have been interpreted in terms of the monomer–monomer stretching frequency and give ω=150 cm−1.

Stabilization and Structure Calculations for Noncovalent Interactions in Extended Molecular Systems Based on Wave Function and Density Functional Theories

2010-05-20

Kevin E. Riley , Michal Pitoňák , Petr Jurečka +1 more

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTStabilization and Structure Calculations for Noncovalent Interactions in Extended Molecular Systems Based on Wave Function and Density Functional TheoriesKevin E. Riley⊥†, Michal Pitoňák⊥‡§, Petr Jurečka⊥∥, and Pavel … ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTStabilization and Structure Calculations for Noncovalent Interactions in Extended Molecular Systems Based on Wave Function and Density Functional TheoriesKevin E. Riley⊥†, Michal Pitoňák⊥‡§, Petr Jurečka⊥∥, and Pavel Hobza*‡∥View Author Information Department of Chemistry, University of Puerto Rico, Rio Piedras, Puerto Rico 00931, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, 166 10 Prague, Czech Republic, Department of Physical and Theoretical Chemistry, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovak Republic, and Department of Physical Chemistry, Palacký University, 771 46 Olomouc, Czech Republic* To whom correspondence should be addressed. E-mail: [email protected]. Phone: +420 220 410 311. Fax: +420 220 410 320.⊥These authors contributed equally to this work and should be considered co-first authors.†University of Puerto Rico.‡Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems.§Comenius University.∥Palacký University.Cite this: Chem. Rev. 2010, 110, 9, 5023–5063Publication Date (Web):May 20, 2010Publication History Received19 January 2010Published online20 May 2010Published inissue 8 September 2010https://pubs.acs.org/doi/10.1021/cr1000173https://doi.org/10.1021/cr1000173review-articleACS PublicationsCopyright © 2010 American Chemical SocietyRequest reuse permissionsArticle Views7851Altmetric-Citations684LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Basis sets,Colloids,Interaction energies,Noncovalent interactions Get e-Alerts

Spectroscopic Studies of the Hydrogen Bond. II. The Shift of the O–H Vibrational Frequency in the Formation of the Hydrogen Bond

1937-11-01

Richard M. Badger , S. H. Bauer

The association spectra of a number of acids and alcohols in the region λλ9000–11,000 have been observed both in solution and in the pure liquids. In each case a broad … The association spectra of a number of acids and alcohols in the region λλ9000–11,000 have been observed both in solution and in the pure liquids. In each case a broad band with maximum near λ10,000 was observed while in the alcohols an additional weaker band near λ9000 appears to be present. Evidence is presented that the λ10,000 band is to be identified with the O–H group. This evidence includes the behavior of the association band with change in concentration and temperature and its presence in several substances in which absorption other than that due to the O–H group is practically absent in the region studied. New evidence is given that a weak intermolecular hydrogen bond is formed between acetone and methyl alcohol. It is pointed out that the presence of absorption in the narrow O–H bands is not to be taken as evidence of the absence of hydrogen bonds in case the absorption is weak. The character of the O–H absorption in the case of intermolecular hydrogen bonds is discussed and the probable nature of the spectrum in the case of an intramolecular bond is indicated. A relation between the energy of the hydrogen bond and the shift of the O–H vibrational frequency is pointed out and its use is suggested in the interpretation of certain spectra.

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Correlation of Rates of Intramolecular Tunneling Processes, with Application to Some Group V Compounds

1960-03-01

R. Stephen Berry

A method is presented whereby the WKB expression for tunneling frequencies permits correlation of these frequencies for members of homologous series of molecules. The necessary data required are the tunneling … A method is presented whereby the WKB expression for tunneling frequencies permits correlation of these frequencies for members of homologous series of molecules. The necessary data required are the tunneling rate for one member of the series, and structural parameters and vibrational frequencies for all members of interest. The method is applied to ND3, NF3, PH3, and AsH3, using NH3 as the molecule whose frequency is known. The method also is used to support the hypothesis that pseudorotation occurs in the trigonal bipyramids PF5 and PCl5.

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On the Quantum Nature of the Shared Proton in Hydrogen Bonds

1997-02-07

Mark E. Tuckerman , Dominik Marx , Michael L. Klein +1 more

The relative influence of thermal and quantum fluctuations on the proton transfer properties of the charged water complexes H 5 O 2 + and H 3 O 2 − was … The relative influence of thermal and quantum fluctuations on the proton transfer properties of the charged water complexes H 5 O 2 + and H 3 O 2 − was investigated with the use of ab initio techniques. These small systems can be considered as prototypical representatives of strong and intermediate-strength hydrogen bonds. The shared proton in the strongly hydrogen bonded H 5 O 2 + behaved in an essentially classical manner, whereas in the H 3 O 2 − low-barrier hydrogen bond, quantum zero-point motion played a crucial role even at room temperature. This behavior can be traced back to a small difference in the oxygen-oxygen separation and hence to the strength of the hydrogen bond.

Molecular Microwave Oscillator and New Hyperfine Structure in the Microwave Spectrum of N<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

1954-07-01

J. P. Gordon , H. J. Zeiger , C. H. Townes

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Partially deuterated water dimers: Microwave spectra and structure

1980-05-01

J. A. Odutola , T. R. Dyke

Radio frequency and microwave spectra for various isotopically substituted water dimers have been studied by molecular beam electric resonance spectroscopy. Resolved radio frequency hyperfine transitions have provided information about the … Radio frequency and microwave spectra for various isotopically substituted water dimers have been studied by molecular beam electric resonance spectroscopy. Resolved radio frequency hyperfine transitions have provided information about the tunneling–rotational levels of water dimer. The microwave spectra have been analyzed with a rigid rotor model to give the following structural information: Roo=2.976 Å (+0.000, −0.030 Å), ϑd=−51(10)°, ϑa=57(10)° and χa=6(20)°. The effects of large amplitude vibrational motion have been estimated and the equilibrium geometry should lie within the above limits. The experimental data is also consistent with χa and φd equal to zero for the equilibrium geometry. The water dimer structure, therefore, has a symmetry plane, a trans configuration, and a linear hydrogen bond within quoted error limits.

Molecular quadrupole moments

1959-01-01

A. D. Buckingham

A. D. Buckingham, Q. Rev. Chem. Soc., 1959, 13, 183 DOI: 10.1039/QR9591300183 A. D. Buckingham, Q. Rev. Chem. Soc., 1959, 13, 183 DOI: 10.1039/QR9591300183

The Bonding of Trihalide and Bifluoride Ions by the Molecular Orbital Method

1951-04-01

George C. Pimentel

A simple molecular orbital treatment is presented to explain the bonding in trihalide ions, X3−, XY2−, and XYZ−, and bifluoride ion, HF2−. The M.O.'s are formed from linear combinations of … A simple molecular orbital treatment is presented to explain the bonding in trihalide ions, X3−, XY2−, and XYZ−, and bifluoride ion, HF2−. The M.O.'s are formed from linear combinations of npσ halogen orbitals, and the 1s hydrogen orbital and stable bonding M.O.'s are obtained without the introduction of higher atomic orbitals. Applications are suggested in prediction of other stable species and low energy reaction intermediates.

A broadband Fourier transform microwave spectrometer based on chirped pulse excitation

2008-05-01

Gordon G. Brown , Brian C. Dian , Kevin O. Douglass +3 more

Designs for a broadband chirped pulse Fourier transform microwave (CP-FTMW) spectrometer are presented. The spectrometer is capable of measuring the 7–18GHz region of a rotational spectrum in a single data … Designs for a broadband chirped pulse Fourier transform microwave (CP-FTMW) spectrometer are presented. The spectrometer is capable of measuring the 7–18GHz region of a rotational spectrum in a single data acquisition. One design uses a 4.2Gsamples∕s arbitrary waveform generator (AWG) to produce a 1μs duration chirped pulse with a linear frequency sweep of 1.375GHz. This pulse is sent through a microwave circuit to multiply the bandwidth of the pulse by a factor of 8 and upconvert it to the 7.5–18.5GHz range. The chirped pulse is amplified by a traveling wave tube amplifier and broadcast inside the spectrometer by using a double ridge standard gain horn antenna. The broadband molecular free induction decay (FID) is received by a second horn antenna, downconverted, and digitized by a 40Gsamples∕s (12GHz hardware bandwidth) digital oscilloscope. The second design uses a simplified pulse generation and FID detection scheme, employing current state-of-the-art high-speed digital electronics. In this spectrometer, a chirped pulse with 12GHz of bandwidth is directly generated by using a 20Gsamples∕s AWG and upconverted in a single step with an ultrabroadband mixer. The amplified molecular emission is directly detected by using a 50Gsamples∕s digital oscilloscope with 18GHz bandwidth. In both designs, fast Fourier transform of the FID produces the frequency domain rotational spectrum in the 7–18GHz range. The performance of the CP-FTMW spectrometer is compared to a Balle–Flygare–type cavity-FTMW spectrometer. The CP-FTMW spectrometer produces an equal sensitivity spectrum with a factor of 40 reduction in measurement time and a reduction in sample consumption by a factor of 20. The CP-FTMW spectrometer also displays good intensity accuracy for both sample number density and rotational transition moment. Strategies to reduce the CP-FTMW measurement time by another factor of 90 while simultaneously reducing the sample consumption by a factor of 30 are demonstrated.

Stereochemistry of reaction paths at carbonyl centres

1974-01-01

H.B. B urgi , Jack D. Dunitz , Jean‐Maríe Lehn +1 more

The halogen bond: an interim perspective

2010-01-01

A. C. Legon

There has been an upsurge of interest in the halogen bond during the last decade. This non-covalent interaction is less familiar than the hydrogen bond, but is similar to it … There has been an upsurge of interest in the halogen bond during the last decade. This non-covalent interaction is less familiar than the hydrogen bond, but is similar to it in several respects. In this article, we first discuss the nature of the halogen bond in the gas phase, as established by systematic investigations of the rotational spectra of complexes B⋯XY, where B is a simple Lewis base and XY is a dihalogen molecule. The geometry of a given B⋯XY is found to be isomorphic with that of the corresponding hydrogen-bonded system B⋯HX, an observation that leads an interim definition of the halogen bond similar to that recently proposed for the hydrogen bond. Selected novel applications of the halogen bond made in the last decade in various areas of chemistry/materials (namely crystal engineering, liquid crystals, nano-materials, polymer chemistry and inorganic chemistry) are then reviewed. These applications generally involve molecules of the type XR (where R is an electron-withdrawing group) acting as the electron donor, rather than dihalogens XY.

Torsion–Vibration–Rotation Interactions in Methanol. I. Millimeter Wave Spectrum

1968-06-15

R. M. Lees , John G. Baker

In a study of internal rotation in methanol, the millimeter wave spectra of CH3OH, CD3OH, and CH3OD have been investigated between 90 and 200 Gc/sec. In the analysis of the … In a study of internal rotation in methanol, the millimeter wave spectra of CH3OH, CD3OH, and CH3OD have been investigated between 90 and 200 Gc/sec. In the analysis of the spectra, torsion–vibration–rotation interactions were treated as adjustable parameters in semiempirical formulas. Kivelson's formula for a-type ΔK = 0 transitions was tested over a wide range of quantum numbers. It reproduced the CH3OH and CD3OH spectra quite well, but the approximations used in the calculations appear to start breaking down for the larger asymmetry of CH3OD. For assignment of b-type ΔK = ± 1 transitions, a method was developed based on the wide spectral range of the millimeter wave spectrometer. Sufficient b-type data were obtained for CH3OH to permit a test of Kirtman's formula for origins of Q branches. Convergence difficulties in the Q-branch least-squares fit prompted a re-examination of the theory, which revealed an interesting linear relation coupling six of the parameters. This relation shows that for any molecule the torsional barrier terms V3 and V6, the two moments of inertia about the near-symmetry axis, and two of the adjustable interaction parameters cannot be independently determined from the spectrum of a single isotopic species. This casts some doubt on values previously reported for V6 in other molecules and adds further uncertainty to V3 determinations. The effective V3 obtained by ignoring torsion–vibration–rotation interactions was found to decrease slightly on deuteration, values of 375.6, 371.8, and 370.3 cm− 1 being obtained for CH3OH, CD3OH, and CH3OD, respectively. Although it is impossible to determine V6 unambiguously from the spectrum of CH3OH alone, a qualitative argument suggests that V6 lies between 0 and −0.8 cm−1. The geometry of the molecule has been completely determined from the experimental data.

Structural chemistry of transition metal complexes of oximes

1974-07-01

Animesh Chakravorty

Fundamental Properties of the CH···O Interaction: Is It a True Hydrogen Bond?

1999-09-25

Yanliang Gu , Tapas Kar , Steve Scheiner

Ab initio calculations are used to analyze the CH···O interaction between FnH3-nCH as proton donor and H2O, CH3OH, and H2CO as acceptor. The interaction is quite weak with CH4 as … Ab initio calculations are used to analyze the CH···O interaction between FnH3-nCH as proton donor and H2O, CH3OH, and H2CO as acceptor. The interaction is quite weak with CH4 as donor but is enhanced by 1 kcal/mol with each F added to the donor. The CH···O interaction behaves very much like a conventional OH···O H-bond in most respects, including shifts in electron density that accompany the formation of the bond and the magnitudes of the various components of the interaction energy. The two sorts of H-bonds also gravitate toward a similar equilibrium geometry and are comparably sensitive to deformations from that structure. In a quantitative sense, while both CH···O and OH···O prefer a linear configuration, the former is somewhat more easily bent and is less sensitive to stretches from its equilibrium H-bond length. Whereas the OH bond has been shown to stretch and undergo a red shift in its vibrational frequency upon formation of a H-bond, the CH bond of the molecules studied here follows the opposite trend, a contraction and a blue shift. Analysis demonstrates that this opposite pattern is not due to any fundamental distinction between the two interactions, since the same sets of forces are acting on both. It is concluded that the CH···O interaction can, indeed, be categorized as a true H-bond.

Molecular structures of gas-phase polyatomic molecules determined by spectroscopic methods

1979-07-01

Marlin D. Harmony , Victor W. Laurie , Robert L. Kuczkowski +5 more

Spectroscopic data related to the structures of polyatomic molecules in the gas phase have been reviewed, critically evaluated, and compiled. All reported bond distances and angles have been classified as … Spectroscopic data related to the structures of polyatomic molecules in the gas phase have been reviewed, critically evaluated, and compiled. All reported bond distances and angles have been classified as equilibrium (re), average (rz), substitution (rs), or effective (ro) parameters, and have been given a quality rating which is a measure of the parameter uncertainty. The surveyed literature includes work from all of the areas of gas-phase spectroscopy from which precise quantitative structural information can be derived. Introductory material includes definitions of the various types of parameters and a description of the evaluation procedure.

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Tables of molecular vibrational frequencies. Consolidated volume II

1977-07-01

Takehiko Shimanouchi

The compilations of fundamental vibrational frequencies of molecules previously published as Tables of Molecular Vibrational Frequencies Part 5, Part 6, Part 7, and Part 8, which appeared in the Journal … The compilations of fundamental vibrational frequencies of molecules previously published as Tables of Molecular Vibrational Frequencies Part 5, Part 6, Part 7, and Part 8, which appeared in the Journal of Physical and Chemical Reference Data in 1972, 1973, and 1974, have been revised. This Consolidated Volume II includes data on a total of 212 molecules in addition to those on 223 molecules included in Volume 1 (NSRDS-NBS 39). Selected values of the fundamental vibrational frequencies are given for each molecule, together with observed infrared and Raman spectral data and citations to the original literature. The selection of vibrational fundamentals has been based on careful studies of the spectral data and comprehensive normal-coordinate analyses. An estimate of the accuracy of the selected values is included. The tables provide a convenient source of information for those who require vibrational energy levels and related properties in molecular spectroscopy, thermodynamics, analytical chemistry, and other fields of physics and chemistry.

Infrared Spectra of H-Bonded Systems

1968-04-15

Yves Maréchal , Andrzej Witkowski

For the linear triatomic X–H··· system, the separability of the X–H stretching vibrations from the hydrogen bond vibrations is analyzed in the spirit of the adiabatic approximation. The adiabatic wavefunctions … For the linear triatomic X–H··· system, the separability of the X–H stretching vibrations from the hydrogen bond vibrations is analyzed in the spirit of the adiabatic approximation. The adiabatic wavefunctions for X–H stretching vibrations are shown to be suitable functions for the evaluation of the principal factors determining the infrared spectral properties of the actual species of carboxylic acid dimers and imidazole crystal. Theoretical infrared spectra in the X–H stretching region of these systems are then obtained and compared with the experimental ones. The quantitative reconstitution of the experimental spectra and, in particular, the predictions for the effect of isotopic substitution of H by D are confirmed. The principal features of the unusual spectral properties of the X–H stretching vibrations in hydrogenbonded systems seem therefore to result from a somewhat peculiar coupling mechanism suggested in the theory.

Relaxation of conformers and isomers in seeded supersonic jets of inert gases

1990-09-01

Rodney S. Ruoff , T. D. Klots , T. Emilsson +1 more

We have studied the relaxation of conformers and the formation/relaxation of isomeric, weakly bonded dimers in pulsed supersonic expansions of seeded inert gases (He, Ne, Ar, Kr). The relaxation was … We have studied the relaxation of conformers and the formation/relaxation of isomeric, weakly bonded dimers in pulsed supersonic expansions of seeded inert gases (He, Ne, Ar, Kr). The relaxation was determined from the intensity of a rotational transition for the higher energy species as a function of carrier gas composition, using the Balle/Flygare Fourier transform microwave spectrometer. Of thirteen molecules with rotational conformers which we examined, those with barriers to internal rotation greater than 400 cm−1 did not relax significantly in any of the carriers. The higher energy forms of ethyl formate, ethanol, and isopropanol, with smaller barriers, were not relaxed by He; those of ethanol and isopropanol were somewhat relaxed by Ne; and all were completely relaxed by as little as 5 to 20 mole percent of Ar or Kr in He or Ne. The relaxation in He or Ne is first order in the concentration of added Ne, Ar, or Kr as well as in the concentration of the high energy conformer. The pseudo first-order rate constants (larger in Ne than in He) increase sharply with Z of the rare gas, roughly in a 0:1:2:4 progression for He, Ne, Ar, and Kr, suggesting that the relaxation involves relatively long-range polarization effects. Similar behavior was found in the formation/relaxation of the weakly bonded dimer pairs: linear OCO–HCN, T-shaped HCN–CO2; linear FH–NNO and bent NNO–HF; and bent HF–DF and DF–HF. The case of the HCN/CO2 dimers is particularly striking. The T-shaped dimer was found first, using Ar as the carrier gas. Five years later the linear form was found with first run neon as carrier, but it could not be detected at all with Ar as the carrier. These results show that in favorable cases high energy species can be studied in supersonic expansions by freezing out a ‘‘high-temperature’’ concentration with a nonrelaxing carrier gas.

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Size-Specific Infrared Spectra of Benzene-(H 2 O) n Clusters ( n = 1 through 7): Evidence for Noncyclic (H 2 O) n Structures

1994-07-01

R. Nathaniel Pribble , Timothy S. Zwier

Resonant ion-dip infrared spectroscopy has been used to record size-specific infrared spectra of C 6 H 6 -(H 2 O) n clusters with n = 1 through 7 in the … Resonant ion-dip infrared spectroscopy has been used to record size-specific infrared spectra of C 6 H 6 -(H 2 O) n clusters with n = 1 through 7 in the O—H stretch region. The O—H stretch spectra show a dramatic dependence on cluster size. For the n = 3 to 5 clusters, the transitions can be divided into three types—attributable to free, π hydrogen-bonded, and single donor water-water O—H stretches—consistent with a C 6 H 6 -(H 2 O) n structure in which benzene is on the surface of a cyclic (H 2 O) n cluster. In n = 6 and 7 clusters, the spectra show distinct new transitions in the 3500 to 3600 wave number region. After comparison of these results with the predictions of ab initio calculations on (H 2 O) n clusters, these new transitions have been assigned to double donor O—H stretches associated with the formation of a more compact, noncyclic structure beginning with (H 2 O) 6 . This is the same size cluster for which ab initio calculations predict that a changeover to noncyclic (H 2 O) n structures will occur.

Nonbonded Potential Parameters Derived from Crystalline Hydrocarbons

1967-12-01

Donald E. Williams

The previously described least-squares derivation of nonbonded potential parameters from crystalline aromatic hydrocarbons was extended to include nonaromatic hydrocarbons. Further evidence was obtained that no specially large energy effects are … The previously described least-squares derivation of nonbonded potential parameters from crystalline aromatic hydrocarbons was extended to include nonaromatic hydrocarbons. Further evidence was obtained that no specially large energy effects are present in the aromatic crystal structures with their π-electron systems. A better separation of the nonbonded energy into C···C, C···H, and H···H components was obtained when the observational equations for the aromatic and nonaromatic structures were combined. The potentials obtained from the combined observational equations gave better fits to the nonaromatics than to the aromatics. Evidence is presented favoring an H–C–H angle of less than 106° in crystalline n-pentane and n-hexane. The parallel packing of molecular chains in the n-hexane crystal and the nonparallel packing in the n-pentane crystal were reproduced by a steepest descent minimization of the lattice energy using the observed lattice constants.

The Grotthuss mechanism

1995-10-01

Noam Agmon

Natural bond orbital analysis of near-Hartree–Fock water dimer

1983-03-15

Alan E. Reed , Frank Weinhold

We have carried out a natural bond orbital analysis of hydrogen bonding in the water dimer for the near‐Hartree–Fock wave function of Popkie, Kistenmacher, and Clementi, extending previous studies based … We have carried out a natural bond orbital analysis of hydrogen bonding in the water dimer for the near‐Hartree–Fock wave function of Popkie, Kistenmacher, and Clementi, extending previous studies based on smaller basis sets and less realistic geometry. We find that interactions which may properly be described as ''charge transfer'' (particularly the n‐σ*OH interaction along the H‐bond axis) play a critical role in the formation of the hydrogen bond, and without these interactions the water dimer would be 3–5 kcal/mol repulsive at the observed equilibrium distance. We discuss this result in relationship to Klemperer's general picture of the bonding in van der Waals molecules, and to previous theoretical analyses of hydrogen bonding by the method of Kitaura and Morokuma.

Determination of Molecular Structure from Microwave Spectroscopic Data

1953-01-01

J. Kraitchman

A method is described for determining the position of an atom in a molecule from spectroscopic measurements on two isotopic species of the molecule. The method is applied to various … A method is described for determining the position of an atom in a molecule from spectroscopic measurements on two isotopic species of the molecule. The method is applied to various types of molecules; explicit expressions are derived for linear, symmetric top, planar, and nonplanar asymmetric top molecules. The number of isotopic species on which measurements must be made to complete the structural determination, i.e., determine the position of every atom in the molecule, is discussed for various types of molecules. An application of the method to the determination of mass difference ratios is also considered.

Evaluated Gas Phase Basicities and Proton Affinities of Molecules; Heats of Formation of Protonated Molecules

1984-07-01

Sharon G. Lias , Joel F. Liebman , R. Levin

The available data on gas phase basicities and proton affinities of molecules are compiled and evaluated. Tables giving the molecules ordered (1) according to proton affinity and (2) according to … The available data on gas phase basicities and proton affinities of molecules are compiled and evaluated. Tables giving the molecules ordered (1) according to proton affinity and (2) according to empirical formula, sorted alphabetically are provided. The heats of formation of the molecules and the corresponding protonated species are also listed.

Radiofrequency and Microwave Spectrum of the Hydrogen Fluoride Dimer; a Nonrigid Molecule

1972-03-01

T. R. Dyke , Brian J. Howard , William Klemperèr

The radiofrequency and microwave spectra of the K=0 states of (HF)2, (DF)2, and HFDF have been studied by the molecular beam electric resonance method. A unique hydrogen tunnelling motion involving … The radiofrequency and microwave spectra of the K=0 states of (HF)2, (DF)2, and HFDF have been studied by the molecular beam electric resonance method. A unique hydrogen tunnelling motion involving the breaking and reforming of the hydrogen bond causes a splitting of rotational energy levels for (HF)2 and (DF)2, but not for HFDF. The electric dipole selection rules and nuclear spin statistics for the tunnelling molecules have been derived from a consideration of an extended permutation-inversion group. Rotational constants, tunneling doublings, electric dipole moments, and deuterium quadrupole coupling constants have been determined from the observed spectra of the K=0 states. (HF)2(DF)2HFDF(B+C)/2 (MHz)6504.8±2.06252.194±0.0026500.1±0.1ν (MHz)19 776±121579.877 ±0.004μa (D)2.987±0.0032.9919±0.00063.029±0.003(eqQ)Da (KHz)···110±8270±30These results are interpreted with a semirigid, nonlinear model of the dimer geometry. The F—F distance is 2.79 ± 0.05 Å, and the end hydrogen fluoride unit is bent from 60 to 70° from the F—F axis. Large amplitude motion of the hydrogen and deuterium atoms occurs. Higher hydrogen fluoride polymers have been studied by mass spectroscopy and electric deflection methods. All were observed to be nonpolar which is interpreted to imply cyclic structures.

The Cologne Database for Molecular Spectroscopy, CDMS: a useful tool for astronomers and spectroscopists

2005-02-21

H. S. P. Müller , F. Schlöder , J. Stützki +1 more

Anharmonic force constant calculations

1972-12-01

A.R. Hoy , I.M. Mills , G. Strey

The relationship of the anharmonic force constants in curvilinear internal coordinates to the observed vibration-rotation spectrum of a molecule is reviewed. A simplified method of setting up the required non-linear … The relationship of the anharmonic force constants in curvilinear internal coordinates to the observed vibration-rotation spectrum of a molecule is reviewed. A simplified method of setting up the required non-linear coordinate transformations is described: this makes use of an L tensor, which is a straightforward generalization of the L matrix used in the customary description of harmonic force constant calculations. General formulae for the L tensor elements, in terms of the familiar L matrix elements, are presented. The use of non-linear symmetry coordinates and redundancies are described. Sample calculations on the water and ammonia molecules are reported.

Benzene Forms Hydrogen Bonds with Water

1992-08-14

Sakae Suzuki , Peter G. Green , Roger E. Bumgarner +3 more

Fully rotationally resolved spectra of three isotopic species of 1:1 clusters of benzene with water (H 2 O, D 2 O, and HDO) were fit to yield moments of inertia … Fully rotationally resolved spectra of three isotopic species of 1:1 clusters of benzene with water (H 2 O, D 2 O, and HDO) were fit to yield moments of inertia that demonstrate unambiguously that water is positioned above the benzene plane in nearly free internal rotation with both hydrogen atoms pointing toward the π cloud. Ab initio calculations (MP2 level of electron correlation and 6-31 G ** basis set with basis set superposition error corrections) predict a binding energy D e ≳ 1.78 kilocalories per mole. In both the experimental and theoretical structures, water is situated nearly 1 angstrom within the van der Waals contacts of the monomers, a clear manifestation of hydrogen bond formation in this simple model of aqueous-π electron interactions.

Complex Organic Interstellar Molecules

2009-08-20

Eric Herbst , E. F. van Dishoeck

Of the over 150 different molecular species detected in the interstellar and circumstellar media, approximately 50 contain 6 or more atoms. These molecules, labeled complex by astronomers if not by … Of the over 150 different molecular species detected in the interstellar and circumstellar media, approximately 50 contain 6 or more atoms. These molecules, labeled complex by astronomers if not by chemists, all contain the element carbon and so can be called organic. In the interstellar medium, complex molecules are detected in the denser sources only. Although, with one exception, complex molecules have only been detected in the gas phase, there is strong evidence that they can be formed in ice mantles on interstellar grains. The nature of the gaseous complex species depends dramatically on the source where they are found: in cold, dense regions they tend to be unsaturated (hydrogen-poor) and exotic, whereas in young stellar objects, they tend to be quite saturated (hydrogen-rich) and terrestrial in nature. Based on both their spectra and chemistry, complex molecules are excellent probes of the physical conditions and history of the sources where they reside. Because they are detected in young stellar objects, complex molecules are expected to be common ingredients for new planetary systems. In this review, we discuss both the observation and chemistry of complex molecules in assorted interstellar regions in the Milky Way.

Implementation of ultrasoft pseudopotentials inab initiomolecular dynamics

1991-03-15

Kari Laasonen , Roberto Car , Changyol Lee +1 more

A scheme for the construction of ultrasoft separable pseudopotentials recently proposed by Vanderbilt is tested in the context of Car-Parrinello ab initio molecular-dynamics calculations on atoms and molecules. For the … A scheme for the construction of ultrasoft separable pseudopotentials recently proposed by Vanderbilt is tested in the context of Car-Parrinello ab initio molecular-dynamics calculations on atoms and molecules. For the case of oxygen, the transferability of the pseudopotential is demonstrated by comparing the calculated properties of molecular ${\mathrm{O}}_{2}$ and ${\mathrm{O}}_{3}$ with those obtained from conventional approaches. Converged results are obtained using plane-wave-basis cutoffs of only \ensuremath{\sim}25 Ry. Forces can be calculated efficiently, and a molecular-dynamics simulation of molecular vibration is demonstrated.

The UMIST database for astrochemistry 2006

2007-02-05

Joanna Woodall , M. Agúndez , A. J. Markwick-Kemper +1 more

Aims.We present a new version of the UMIST Database for Astrochemistry, the fourth such version to be released to the public. The current version contains some 4573 binary gas-phase reactions, … Aims.We present a new version of the UMIST Database for Astrochemistry, the fourth such version to be released to the public. The current version contains some 4573 binary gas-phase reactions, an increase of 10% from the previous (1999) version, among 420 species, of which 23 are new to the database.

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Microwave Spectroscopy

1956-04-01

C. H. Townes , A. L. Schawlow , Norman F. Ramsey

First Page First Page

Molecular Vibrational—Rotational Spectra

1983-10-01

W.J.O.-T.

Handbook of High‐resolution Spectroscopy

2011-06-28

Martin Qüack , F. Merkt

The field of High-Resolution Spectroscopy has been considerably extended and even redefined in some areas. Combining the knowledge of spectroscopy, laser technology, chemical computation, and experiments, Handbook of High-Resolution Spectroscopy … The field of High-Resolution Spectroscopy has been considerably extended and even redefined in some areas. Combining the knowledge of spectroscopy, laser technology, chemical computation, and experiments, Handbook of High-Resolution Spectroscopy provides a comprehensive survey of the whole field as it presents itself today, with emphasis on the recent developments. This essential handbook for advanced research students, graduate students, and researchers takes a systematic approach through the range of wavelengths and includes the latest advances in experiment and theory that will help and guide future applications. * The first comprehensive survey in high-resolution molecular spectroscopy for over 15 years * Brings together the knowledge of spectroscopy, laser technology, chemical computation and experiments * Brings the reader up-to-date with the many advances that have been made in recent times * Takes the reader through the range of wavelengths, covering all possible techniques such as Microwave Spectroscopy, Infrared Spectroscopy, Raman Spectroscopy, VIS, UV and VUV * Combines theoretical, computational and experimental aspects * Has numerous applications in a wide range of scientific domains * Edited by two leaders in this field * Provides an overview of rotational, vibration, electronic and photoelectron spectroscopy Volume 1 - Introduction: Fundamentals of Molecular Spectroscopy Volume 2 - High-Resolution Molecular Spectroscopy: Methods and Results Volume 3 - Special Methods & Applications

Rotational Spectra of Interstellar Cyanopolyyne HC2n+1N (n=0-8) Neutrals and Cations

2025-06-24

Yihong Wang , Qi Lin , Huaping Xiao +1 more | Research in Astronomy and Astrophysics

Abstract We obtain the rotational spectra for cyanopolyynes HC$_{2n+1}$N ($n=0-8$) and their cations through quantum chemical calculations. Rotational constants, quartic centrifugal distortion constants, and hyperfine constants are calculated. The rotational … Abstract We obtain the rotational spectra for cyanopolyynes HC$_{2n+1}$N ($n=0-8$) and their cations through quantum chemical calculations. Rotational constants, quartic centrifugal distortion constants, and hyperfine constants are calculated. The rotational constants are determined at the theoretical level of B3PW91/cc-pVTZ, incorporating with the calibration for the moment of inertia. It significantly improves the accuracy with respect to the uncalibrated ones. Quartic centrifugal distortion constants are estimated using the empirical relation, achieving an accuracy of $\sim$0.02\% with respect to the experiment. Hyperfine constants are computed at the B3PW91/6-311+G(df, pd) and B3PW91/aug-cc-PVTZ levels. The overall frequency characteristics of all the target molecules are discussed and their detectability in the ISM is also quantitatively evaluated. The rotational spectra of selected species (HC$_{13}$N, HC$_{15}$N, HC$_{17}$N, and HC$_5$N$^+$) are reproduced, showing satisfied consistency with experiments or observations. Our results provide useful reference for observations and experiments, even that more advanced calculation levels and basis sets are required to achieve better accuracy.

Theoretical insights on the structure and stability of the [C2, H3, P, O] isomeric family

2025-06-23

Carmen Barrientos , Miguel Sanz‐Novo , Clara I. Sá‎nchez +2 more | Pure and Applied Chemistry

Abstract Phosphorus is a crucial biogenic element, yet its astrochemical role remains poorly understood due to its low cosmic abundance and the limited number of detected P-containing molecules in the … Abstract Phosphorus is a crucial biogenic element, yet its astrochemical role remains poorly understood due to its low cosmic abundance and the limited number of detected P-containing molecules in the interstellar medium. Given its significance for prebiotic chemistry, PCO-bearing molecules, such as the phosphorus analogs of isocyanates, are promising candidates for laboratory and interstellar studies. Herein, we present a comprehensive theoretical study on the isomeric landscape of the C 2 H 3 PO system, identifying and characterizing 24 low-lying isomers through high-level quantum chemical calculations. The study employs double-hybrid DFT and coupled-cluster methods to refine energy values and structural parameters, while topological analysis of electronic density characterizes chemical bonding. Vinylphosphinidene oxide (CH 2 CHPO) emerges as the most stable isomer, followed by methylphosphaketene (CH 3 PCO), with oxygen-bound structures playing a crucial role in stability. Comparisons with the C 2 H 3 NO system reveal structural parallels, reinforcing the importance of oxygen-bound species. Cyclic structures were also explored, with three- and four-membered P- and O-heterocycles identified, although they are generally less stable than open-chain isomers. These results provide insights into the chemical behavior and stability of C 2 H 3 PO isomers, which could help future spectroscopic studies and detection efforts in the interstellar medium.

Ab initio study of interstellar molecule HOCN and DOCN: a comparative analysis of potential energy surface properties and vibrational spectrum

2025-06-20

Yapeng Fang , Yuyang Zhang , Nana Jia +3 more | Physica Scripta

Abstract Cyanic acid, HOCN, has been detected in the giant molecular cloud SgrB2, however, there is a lack of experimental data that could assist future spectroscopy studies. To address this … Abstract Cyanic acid, HOCN, has been detected in the giant molecular cloud SgrB2, however, there is a lack of experimental data that could assist future spectroscopy studies. To address this issue, HOCN and its isotopic molecule DOCN were calculated using the ab initio method based on the CCSD(T)-F12/cc-pVQZ level of theory. First, the molecular structures were optimized geometrically. Subsequently, an iterative algorithm was used to calculate one-dimensional (1D) and two-dimensional (2D) potential energy surfaces (PES) until the convergence threshold was reached, and the PES images were fitted. Based on this, the anharmonic frequencies were obtained using the vibrational self-consistent field (VSCF) and vibrational configuration interaction (VCI) methods, respectively. The calculated values of the fundamental frequencies were found to be in good agreement with the reference values. Finally, the obtained anharmonic vibrational frequencies were used to simulate the IR spectra. In addition, the Fermi resonance phenomenon among anharmonic frequencies can enhance the absorption intensity between overtones and combination frequencies. This study provides valuable insights into the internal characteristics of interstellar molecules and serves as a reference for both molecular spectroscopy research and interstellar molecular research.

Conformational Analysis of Neutral and Ionic Arginine Forms Using DFT Methods

2025-06-19

Fulya Çağlar , Gökhan Aksoy , Cenk Selçuki | ACS Omega

From Norbornadiene to Norcamphor and Camphor: Reduced-Cost Semiexperimental Structural Refinement from Limited Isotopologue Data

2025-06-18

Lina Uribe , Marco Mendolicchio , Sofía Municio +5 more | The Journal of Physical Chemistry Letters

We present an efficient semiexperimental protocol for determining spectroscopically accurate molecular structures from limited isotopologue data with a focus on medium-sized organic molecules. The availability of all monosubstituted isotopologues of … We present an efficient semiexperimental protocol for determining spectroscopically accurate molecular structures from limited isotopologue data with a focus on medium-sized organic molecules. The availability of all monosubstituted isotopologues of norbornadiene enabled the determination of a complete semiexperimental (reqSE) equilibrium structure, establishing a reference for validating reduced-dimensionality approaches that avoid deuterium substitution. The rotational spectrum of norcamphor is reported here for the first time, providing a critical benchmark for assessing the method's accuracy. By combining composite quantum-chemical calculations with a cost-effective vibrational correction scheme, the protocol achieves near-spectroscopic accuracy while substantially reducing the computational effort. This approach enables the structural characterization of large systems where extensive isotopic substitution is impractical, thereby broadening the applicability of semiexperimental methods in modern molecular spectroscopy.

Probing Hydrogen-Bonding Preferences and Methyl Internal Rotation in Sotolon and Sotolon-(H2O)1,2

2025-06-17

Andrés Verde , Juan C. López , Susana Blanco | International Journal of Molecular Sciences

Sotolon is a chiral furanone derivative featuring three distinct oxygen atoms at carbonyl, hydroxyl, and cyclic ether groups that can serve as hydrogen-bond acceptor sites, making it an ideal model … Sotolon is a chiral furanone derivative featuring three distinct oxygen atoms at carbonyl, hydroxyl, and cyclic ether groups that can serve as hydrogen-bond acceptor sites, making it an ideal model system for probing water's preferential interactions with competing functional groups. In this study, the rotational spectrum of sotolon and its microsolvated complexes, representing the early stages of hydration, was investigated using chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The conformational landscape of sotolon is dominated by a single conformer stabilized by an intramolecular O-H···O=C hydrogen bond. During hydration, water molecules disrupt this interaction by forming closed hydrogen-bonded cycles, resulting in mono- and dihydrated complexes. High-level theoretical calculations underscore the central role of electrostatic interactions in stabilizing these hydrated structures. Furthermore, A/E splittings observed in the rotational spectrum, arising from the internal rotation of one of sotolon's methyl groups, provide insight into how hydration modulates the methyl internal rotation barrier.

Rotational investigation of volatile anesthetics: Conformational equilibrium, molecular structure, and complex hyperfine interactions of methoxyflurane

2025-06-16

Sven Herbers , Wenqin Li , Philipp Buschmann +3 more | The Journal of Chemical Physics

The volatile anesthetic methoxyflurane was investigated in the 2–8 GHz region by chirp-excitation Fourier-transform broadband microwave spectroscopy. The presence of two conformers—gauche–trans (C1) and trans–trans (Cs)—each containing two quadrupolar chlorine … The volatile anesthetic methoxyflurane was investigated in the 2–8 GHz region by chirp-excitation Fourier-transform broadband microwave spectroscopy. The presence of two conformers—gauche–trans (C1) and trans–trans (Cs)—each containing two quadrupolar chlorine nuclei and one methyl internal rotor, results in a very dense spectrum with complex rotational hyperfine effects, where contributions from nuclear quadrupole interactions and internal rotation couple to the overall molecular rotation. For the spectrally more complicated C1-conformer, additional impulse-excitation cavity measurements were carried out in the region of 10–21 GHz. To the best of our knowledge, there is no published code that can handle two quadrupolar nuclei in a non-coplanar orientation with respect to the internal rotor, so we developed our own codes interfacing with Pickett’s SPFIT rovibrational fitting program to allow for a near-experimental accuracy fit of the relatively abundant isotopologues, comprising all isotopologue combinations of the 35Cl and 37Cl nuclei. Furthermore, the Hartwig–Herbers’ XIAM-NQ code was later extended to treat a second quadrupolar nucleus, and global fits with this new code XIAM-2NQ were validated against SPFIT results. The relative transition intensities of the two conformers were used to estimate the relative room-temperature population as N(Cs)/N(C1) = 0.88 ± 0.30 corresponding to a difference in the Gibbs free energy of −1.4 ± 1.1 kJ/mol. A computational characterization using density functional theory [CAM-B3LYP-D3 (BJ)] complemented the experimental results. This work completes the rotational investigations on the conformational and structural panorama of the most important halogenated inhalational anesthetics, potentially enabling their monitoring through rotational spectroscopic fingerprints.

Conformations and Structures of 3-Oxopentanenitrile and 4-Methyl-3-oxopentanenitrile Revealed by Rotational Spectroscopy

2025-06-13

Yan Feng , Yuting Li , Fang Shen +4 more | The Journal of Physical Chemistry A

The conformations and molecular structures of two cyano-substituted ketones, namely 4-methyl-3-oxopentanenitrile (MPN) and 3-oxopentanenitrile (PN), have been investigated by using supersonic jet Fourier transform microwave (FTMW) spectroscopy. The rotational spectrum … The conformations and molecular structures of two cyano-substituted ketones, namely 4-methyl-3-oxopentanenitrile (MPN) and 3-oxopentanenitrile (PN), have been investigated by using supersonic jet Fourier transform microwave (FTMW) spectroscopy. The rotational spectrum of a single conformation was measured and assigned for 4-methyl-3-oxopentanenitrile (MPN-I) and 3-oxopentanenitrile (PN-I), respectively. Additional measurements were conducted for 13C and 15N singly substituted isotopologues of conformer PN-I in natural abundance. The comprehensive rotational spectroscopic investigations yield accurate values for the rotational constants and 14N quadrupole coupling constants, which facilitate the structural elucidations of the observed conformers. For conformer PN-I, the near constancy of the Pcc values upon isotopic substitution indicates that the heavy atoms of this conformation are closely located to the ab-plane. Quantum chemical calculations, noncovalent interaction analysis, and molecular electrostatic surface potentials provide further insight into the energetics and structures of the two molecules.

Electron scattering from oxetane and thietane and their isomers

2025-06-12

Sudhanshu Arya , Bobby Antony | Journal of Applied Physics

We performed quantum mechanical calculations of electron scattering from four-membered heterocycles containing oxygen and sulfur, namely, oxetane (trimethylene oxide) and thietane (trimethylene sulfide), along with their isomers, focusing on the … We performed quantum mechanical calculations of electron scattering from four-membered heterocycles containing oxygen and sulfur, namely, oxetane (trimethylene oxide) and thietane (trimethylene sulfide), along with their isomers, focusing on the electron-impact energy range of 15–5000 eV. These compounds hold considerable significance in astrochemistry, atmospheric chemistry, and pharmaceutical science, as well as crucial roles in biological and industrial processes. We used the complex optical-potential model with screening correction to find the total, inelastic, and elastic cross sections. Ionization cross sections were derived through the semiempirical complex scattering potential-ionization contribution method from inelastic cross-sectional data. Our results exhibit strong agreement with the available theoretical predictions and the experimental data. This study marks the first analysis of most of the molecules investigated. Furthermore, a comparative analysis of isomeric forms and the heteroatom composition is reported to assess the impact of electronic-structural variations on scattering behavior.

Submillimeterwave Spectroscopy of and Interstellar Search for Nitrosomethane: CH3NO

2025-06-12

L. Margulès , Zachary T. P. Fried , Alex N. Byrne +4 more | The Astrophysical Journal

Abstract New measurements of nitrosomethane (CH 3 NO), a formamide isomer, were done up to 660 GHz. The molecule exhibits internal rotation motion from the CH 3 group, and therefore … Abstract New measurements of nitrosomethane (CH 3 NO), a formamide isomer, were done up to 660 GHz. The molecule exhibits internal rotation motion from the CH 3 group, and therefore the analysis with a dedicated rho-axis method code, RAM36, was used. A total of 2035 lines for v t = 0 and 1 states of A and E symmetries were fitted with an rms deviation of 41.1 kHz, with the maximum quantum numbers values J = 30 and K a = 15. Using these new data, CH 3 NO was searched in the cold dark cloud Taurus Molecular Cloud 1 as well as the high mass star-forming regions Sgr B2(N) and NGC 6334I. CH 3 NO was not observed in any of the sources, 3 σ column density upper limits were determined, and we discuss the implications for the chemistry of CH 3 NO in the interstellar medium. The accurate spectroscopic prediction of its spectra provided in this work will allow astronomers to continue the search of CH 3 NO in other interstellar sources.

Comparison of the CH and OH Groups as Proton Donors within Hydrogen Bonds

2025-05-28

Savannah Rawlings , Steve Scheiner | ChemistryEurope

The ability of the CH group to act as proton donor is now widely accepted, even if the H bonds (HBs), which it forms are typically much weaker than those … The ability of the CH group to act as proton donor is now widely accepted, even if the H bonds (HBs), which it forms are typically much weaker than those of the hydroxyl group, particularly for a sp 3 ‐hybridized C. An NH 3 nucleophile is allowed to approach both the terminal methyl group and the hydroxyl of n‐butanol, so as to form either a CH··N or OH··N HB. Density functional theory calculations show that the latter is much stronger than the former. However, the strength of the CH··N HB can be amplified and approach much closer to that of OH··N by appropriate placement of suitable electron‐withdrawing and donating substituents on the butanol. The interaction energy of the CH··N HB reaches above 6–8 kcal mol −1 in several cases, considerably larger than the prototype HB within the water dimer.

Formally Stereoretentive SN1 Reactions of Homoallylic Tertiary Alcohols Via Nonclassical Carbocation

2025-05-27

Kaushalendra Patel , Leonie Wilczek , Francesco Calogero +1 more

We present a stereoretentive nucleophilic substitution of homoallylic tertiary alcohols via the formation of a nonclassical cyclopropyl carbinyl (CPC) carbocation intermediate. This strategy enables the creation of highly congested tertiary … We present a stereoretentive nucleophilic substitution of homoallylic tertiary alcohols via the formation of a nonclassical cyclopropyl carbinyl (CPC) carbocation intermediate. This strategy enables the creation of highly congested tertiary centers with preserved stereocontrol, addressing the typical challenges of carbocation instability and reactivity in SN1 mechanisms. The stabilization of the CPC intermediate is crucial for achieving precise regio- and stereoselectivity, significantly enhancing the utility of SN1-type mechanisms in complex molecule synthesis.

Influence of Dielectric constant on Protonation Equilibria of L-Cysteine and L-Methionine in 1, 4-Dioxane-Water Mixture

2025-05-27

K. Bharath Kumar Naik | Global research and development journal for engineering.

Hydrogen Bond Interaction Networks in the Mixed Pentamers of Hydrogen Sulfide and Water

2025-05-26

Pablo Pinacho , Cristóbal Pérez , Marcel Stahn +5 more

The observation of gas-phase water clusters has been instrumental in understanding water aggregation and cooperativity, paving the way for solvation models in the bulk. However, the characterization of hydrogen sulfide … The observation of gas-phase water clusters has been instrumental in understanding water aggregation and cooperativity, paving the way for solvation models in the bulk. However, the characterization of hydrogen sulfide self-aggregation is still largely unexplored. Here, we investigate two mixed pentamers of hydrogen sulfide and water to examine the influence of the weaker, dispersion-based and less directional interactions caused by hydrogen sulfide. Unprecedented structural resolution was obtained by combination of jet-cooled broadband rotational spectroscopy and quantum-chemical calculations. Specifically, we compare the 4:1 and 1:4 hydrogen sulfide - water pentamers, offering comparison with the prototype homoclusters. Important structural differences are revealed in the hydrogen sulfide clusters, which reorganize to compensate for the weaker sulfur-centered hydrogen bonds. The noncovalent interactions in the pentamers were rationalized using density functional theory and reduced electronic density calculations. Moreover, a comprehensive many-body decomposition energy analysis revealed significant variations in molecule two- and three-body contributions to the total interaction energy based on the relative proportions of H2O and H2S. These findings offer new insights into the distinct cooperative forces in water and hydrogen sulfide clusters. The results will improve our understanding and modeling of sulfur-centered hydrogen bonds, which may be useful across various research fields, including protein folding, molecular aggregation, materials science, and computational benchmarking.

Crystal Structures of Water and Tertiary Amines: Hydrates or Ice with a Twist?

2025-05-26

Annika Schmidt , Mara Schöler , Tom Szidat +3 more

Infrared Spectroscopic Identification of Mass-Selected Benzonitrile Ions in Neon Matrices: Astrochemical Implications

2025-05-22

Wen-Jian Huang , Sheng‐Lung Chou , Chih‐Hao Chin +2 more

Benzonitrile (C6H5CN) has emerged as a key astrochemical molecule, yet the vibrational spectra of its ionic forms remain incomplete. In this work, we present the first IR absorption spectra of … Benzonitrile (C6H5CN) has emerged as a key astrochemical molecule, yet the vibrational spectra of its ionic forms remain incomplete. In this work, we present the first IR absorption spectra of mass-selected C6H5CN+ and C6H5CN- isolated in solid neon at 3 K. Distinct vibrational features of both ions were identified through their differential response to IR and UV photolysis and comparison with theoretical predictions of vibrational frequencies and intensities. These results provide valuable spectroscopic benchmarks for the identification of benzonitrile ions in space and highlight the effectiveness of matrix-isolation techniques for resolving the vibrational structures of transient molecular ions relevant to astrochemistry.

Probing the Kinematics of Multiple- and Single-protostar Systems in Perseus with N2H+

2025-05-22

Erica Behrens , Adele Plunkett , Zhi‐Yun Li

Abstract We analyze the dense gas kinematics in two class 0/I protostellar cores, Per 30 and NGC 1333 IRAS 7, in the Perseus Molecular Cloud to determine whether their velocity … Abstract We analyze the dense gas kinematics in two class 0/I protostellar cores, Per 30 and NGC 1333 IRAS 7, in the Perseus Molecular Cloud to determine whether their velocity structures are indicative of rotation. We examine the hyperfine structure of the N 2 H + J = 1–0 transition by combining 3″ (900 au) Atacama Large Millimeter/submillimeter Array measurements with 9″ (2700 au) measurements from the Green Bank Telescope. We use the CASA Feather method to combine these data in order to maximize our sensitivity across spatial scales. We fit the N 2 H + spectra to constrain the centroid velocity of the gas at each pixel and use these values to calculate the linear velocity gradient and specific angular momentum within apertures centered on each protostar with radii ranging from 5″ to 60″. Our results indicate that the velocity structure probed by the N 2 H + emission is likely not a result of core rotation. These findings are consistent with other studies in the literature that indicate rotation is often not evident on scales ≲1000 au. We instead suggest that the velocity structure we see is a result of torques caused by irregular density distributions in these protostellar systems.

Astrochemical Significance of C2H7NO Isomers: A Computational Perspective on Their Stability and Detectability

2025-05-15

Lisset Noriega , Luis Armando González-Ortiz , Filiberto Ortíz‐Chi +1 more

Nitrogen- and oxygen-containing molecules play a key role in interstellar chemistry, particularly as precursors to biologically relevant species such as amino acids. Among the C2H7NO isomers, 2-aminoethanol is the only … Nitrogen- and oxygen-containing molecules play a key role in interstellar chemistry, particularly as precursors to biologically relevant species such as amino acids. Among the C2H7NO isomers, 2-aminoethanol is the only one detected in the ISM. This study systematically explores the C2H7NO chemical space, identifying eight structural isomers, with 1-aminoethanol as the global minimum and methylaminomethanol, 11.5 kcal/mol higher in energy, as a viable higher-energy species. To assess their astrochemical relevance, we conducted a comprehensive conformational analysis and computed rotational constants to guide future spectroscopic searches. These findings provide critical insights into C2H7NO isomers, identifying new candidates for ISM detection and expanding our understanding of nitrogen- and oxygen-containing organic species in space.

Hydration and Conformation of 2-Ethylfuran Explored by Microwave Spectroscopy

2025-05-14

Charlotte N. Cummings , Nicholas R. Walker

Rotational spectra of one conformer of a 2-ethylfuran···H2O complex and two conformers of the isolated 2-ethylfuran molecule have been recorded by chirped-pulse Fourier transform microwave spectroscopy. The species were probed … Rotational spectra of one conformer of a 2-ethylfuran···H2O complex and two conformers of the isolated 2-ethylfuran molecule have been recorded by chirped-pulse Fourier transform microwave spectroscopy. The species were probed while entrained within a gas sample undergoing supersonic expansion. The spectra of five isotopologues of the complex have been analyzed to yield rotational (A0, B0, C0) and centrifugal distortion constants (DJ, DJK, d1) allowing structural parameters to be determined by fitting to the experimentally determined moments of inertia. Quantum chemical calculations have been performed to support the interpretation of the experimental results and gain further insights. 2-Ethylfuran is shown to adopt C1 symmetry within the observed conformer of 2-ethylfuran···H2O with the length of the hydrogen bond, r(Hb···O1), which connects H2O with 2-ethylfuran determined to be 2.0950(42) Å in the r0 geometry. The geometry of the hydrogen bonding interaction deviates from linearity such that the ∠(Ow-Hb···O1) angle (where Ow and O1 are the oxygen atoms of water and furan, respectively) is 167.69(16)° in the r0 geometry. The experimental and theoretical results thus imply the presence of a weak interaction between the oxygen of H2O and the ethyl group within the observed conformer of 2-ethylfuran···H2O. Evidence is presented to suggest that the Cs conformer of the isolated 2-ethylfuran molecule is lower in energy than the C1 conformer implying that the energy ordering of the two lowest-energy conformers of 2-ethylfuran reverses when the isolated molecule is hydrated by a single H2O molecule.

Effects of different temperature, light intensity, and photoperiod on the physiology and biochemistry of Ulva prolifera originating from different reproductive sources

2025-05-09

Xuan Zhou , J. M. Bian , Shenyuan Liang +6 more

Formation of All Three C2H4O Isomers—Ethylene Oxide (c-C2H4O), Acetaldehyde (CH3CHO), and Vinyl Alcohol (CH2CHOH)—in Ethanol-containing Interstellar Analog Ices

2025-05-06

Jia Wang , Chaojiang Zhang , Joshua H. Marks +1 more

Abstract Oxygen-containing complex organic molecules are key precursors to biorelevant compounds fundamental for the origins of life. However, the untangling of their interstellar formation mechanisms has just scratched the surface, … Abstract Oxygen-containing complex organic molecules are key precursors to biorelevant compounds fundamental for the origins of life. However, the untangling of their interstellar formation mechanisms has just scratched the surface, especially for oxygen-containing cyclic molecules. Here, we present the first laboratory simulation experiments featuring the formation of all three C 2 H 4 O isomers—ethylene oxide ( c –C 2 H 4 O), acetaldehyde (CH 3 CHO), and vinyl alcohol (CH 2 CHOH)—in low-temperature model interstellar ices composed of carbon monoxide (CO) and ethanol (C 2 H 5 OH). Ice mixtures were exposed to galactic cosmic-ray proxies with an irradiation dose equivalent to a cold molecular cloud aged (7 ± 2) × 10 5 yr. These biorelevant species were detected in the gas phase through isomer-selective photoionization reflectron time-of-flight mass spectrometry during temperature-programmed desorption. Isotopic labeling experiments reveal that ethylene oxide is produced from ethanol alone, providing the first experimental evidence to support the hypothesis that ethanol serves as a precursor to the prototype epoxide in interstellar ices. These findings reveal feasible pathways for the formation of all three C 2 H 4 O isomers in ethanol-rich interstellar ices, offering valuable constraints on astrochemical models for their formation. Our results suggest that ethanol is a critical precursor to C 2 H 4 O isomers in interstellar environments, representing a critical step toward unraveling the formation mechanisms of oxygen-containing cyclic molecules, aldehydes, and their enol tautomers from alcohols in interstellar ices.

Controlling LiH molecular orientation via rovibrational pre-excitation by utilizing infrared laser pulses and terahertz half-cycle laser pulses

2025-05-06

Qingqing Jia , Yuxin Leng , Hao Li +3 more

Abstract We theoretically investigate the effect of rovibrational pre-excitation on molecular orientation. Infrared laser pulses are employed to manipulate the molecular vibrational wave packet and control the rovibrational transitions of … Abstract We theoretically investigate the effect of rovibrational pre-excitation on molecular orientation. Infrared laser pulses are employed to manipulate the molecular vibrational wave packet and control the rovibrational transitions of LiH molecules. Two rovibrational pre-excitation schemes are proposed to examine the influence of the vibrational quantum number v and rotational quantum number J on the molecular orientation degree. Our results demonstrate that molecular orientation is enhanced when J is constant, and v is increased. When both v and J are varied concurrently, it is found that changes in J have a more significant effect on molecular orientation than changes in v . Additionally, we discuss the impact of the electric field amplitude and carrier-envelope phase in both pre-excitation schemes.

A Pure Rotational Spectroscopic Study of Two Nearly-Equivalent Structures of Hexafluoroacetone Imine, (CF3)C=NH

2025-05-05

Daniel A. Obenchain , Beppo Hartwig , Daniel J. Frohman +5 more

Rotational spectra for hexafluoroacetone imine, the singly substituted 13C isotopologues, and the 15N isotopologue, have been recorded using both cavity and chirped pulse Fourier transform microwave spectrometers. The spectra observed … Rotational spectra for hexafluoroacetone imine, the singly substituted 13C isotopologues, and the 15N isotopologue, have been recorded using both cavity and chirped pulse Fourier transform microwave spectrometers. The spectra observed present as being doubled with separations between each pair of transitions being on the order of a few tens of kilohertz which is consistent with a large amplitude motion producing two torsional substates. The observed splitting is most likely due to the combined motions of the CF3 groups, for which the calculated barrier is small. However, no transitions between states could be observed and, similarly, no Coriolis coupling parameters were required to achieve a satisfactory fit for the transition frequencies. Hence, and somewhat curiously, the two states have been fit independently of each other such that the two states may simply be considered near-equivalent conformers. The structural properties of hexafluoroacetone imine are compared with two isoelectronic molecules hexafluoroisobutene and hexafluoroacetone. Rotational constants, quartic centrifugal distortion constants, and the 14N nuclear electric quadrupole coupling tensor have been determined and are presented together with supporting quantum chemical calculations.

Evidence for Electron Spin-Torsion Coupling in the Rotational Spectrum of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>CH</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:mi>CO</mml:mi></mml:mrow></mml:math> Radical

2025-05-02

L. H. Coudert , Olivier Pirali , Marie‐Aline Martin‐Drumel +4 more

Open-shell nonrigid molecular systems exhibiting an internal rotation are likely candidates for a coupling between the spin angular momentum of the unpaired electron and the torsional motion. This electron spin-torsion … Open-shell nonrigid molecular systems exhibiting an internal rotation are likely candidates for a coupling between the spin angular momentum of the unpaired electron and the torsional motion. This electron spin-torsion coupling lacked both an experimental validation and a theoretical modeling. Here, the first experimental observation of the electron spin-torsion coupling is reported analyzing the pure rotational spectrum at millimeter wavelengths of the CH_{3}CO radical, a ^{2}Σ open-shell molecule displaying an internal rotation of its methyl group. To account for this coupling, a specific Hamiltonian incorporating the rotational, torsional, and electronic degrees of freedom is developed and allows us to reproduce the experimental spectrum. The present demonstration of the electron spin-torsion coupling will undoubtedly be key to future investigations of large open-shell molecules exhibiting a complex internal dynamics.

A re-examination of the highly floppy melamine molecule and predictability of quasi-molecule theory

2025-05-01

A. J. C. Varandas

Passage And Resonance In Synergy – PARIS: A molecular jet chirp- and tone-excitation Fourier transform microwave spectrometer for broad acquisition and high resolution

2025-05-01

Ha Vinh Lam Nguyen , Sven Herbers , X. Landsheere +1 more

Jet-expansion Fourier transform microwave (FTMW) spectroscopy is a powerful technique for investigating isolated molecules and molecular aggregates. The coaxial beam-resonator arrangement offers unrivalled resolution, but requires repetitive frequency retuning of … Jet-expansion Fourier transform microwave (FTMW) spectroscopy is a powerful technique for investigating isolated molecules and molecular aggregates. The coaxial beam-resonator arrangement offers unrivalled resolution, but requires repetitive frequency retuning of a high-Q resonator for survey spectra using short, resonant single-tone excitation pulses. Chirp-excitation methods, using a fast but powerful frequency-ramp signal passing over spectral line positions, dramatically reduce survey time, but at the cost of lower resolution and sensitivity for individual lines. As a consequence, many laboratories employ both spectrometer types. However, setting up individual machines with their own vacuum systems, high-frequency electronics, and control software is costly and time-consuming. We developed and constructed the PARIS (Passage And Resonance In Synergy) FTMW spectrometer, operating in the 2–20 GHz range, integrating both tone-excitation and chirp-excitation techniques in a single, resource-efficient setup: Using a modular design, most electronic components serve dual-purpose, with the integration of reflector-refocused and resonator-enhanced interaction setups in a spherical high-vacuum chamber. The chirp and single-tone excitation setups are arranged perpendicularly, with instant mode-switching, both using microwave propagation coaxial with the molecular jet-expansion. PARIS achieves a sensitivity of a few parts-per-billion for OCS diluted in neon (1%) on the resonator axis and a few parts-per-million on the broadband axis. A resolution (full width at half maximum, FWHM, of the amplitude spectrum) of ∼2 kHz is attained with both experiments, capable of resolving complex hyperfine structures, such as those from two 14N nuclei of 4-methylpyrimidine, already in broadband operation at minimum resolvable peak separation matching the respective FWHM.

Improved spectroscopic parameters and rotational energy structure of the ground vibrational state of AsH<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e34550" altimg="si41.svg"><mml:msub><mml:mrow/><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:math>

2025-05-01

O.N. Ulenikov , E.S. Bekhtereva , O.V. Gromova +3 more

Substituent effects on the solvent power of the haloolefin HCFO-1233 yd.(Z)

2025-05-01

Ao Fan , Hongwei Zhou , Daniel Maksuta +1 more

Thermodynamic Characteristics of Protolytic Equilibriums Involving Tyrosyl-Proline

2025-05-01

П. Д. Крутов , О. Н. Крутова , S. A. Bychkova +3 more

Deciphering the Complexity in the Rotational Spectrum of Deuterated Ethylene Glycol

2025-04-29

Jordan A. Claus , Mattia Melosso , Agathe Maillard +3 more

Ethylene glycol (CH2OH-CH2OH) is an abundant "complex organic molecule" (COM) detected in different astronomical objects, but the steps of its interstellar synthesis are not yet fully understood. In this respect, … Ethylene glycol (CH2OH-CH2OH) is an abundant "complex organic molecule" (COM) detected in different astronomical objects, but the steps of its interstellar synthesis are not yet fully understood. In this respect, the observation of deuterated isotopologues could offer insights into its formation mechanism as well as into its chemical evolution in space. Such observations, however, require detailed spectroscopic knowledge of their rotational features. Here, we present an extensive analysis of the rotational spectrum of oxygen-deuterated ethylene glycol, including the singly and doubly deuterated forms. The new measurements, carried out between 75 and 450 GHz, significantly expand the spectroscopic knowledge of the aGg' conformers of the CH2OH-CH2OD, CH2OD-CH2OH, and CH2OD-CH2OD species. We also report, for the first time, the laboratory identification of the gGg' conformers of the two mono-deuterated species. Our results reveal previously unobserved perturbations arising from the interaction between CH2OH-CH2OD and CH2OD-CH2OH, which has been modeled by including Coriolis coupling and Fermi constants in the Hamiltonian and allowed the accurate determination of the energy difference among them. Additionally, we observed significant anomalies in the spectrum of the doubly deuterated species, which seem to be caused by accidental degeneracies between the levels of the two tunneling substates. Despite the complexity and difficulties, the improved spectroscopic parameters derived from our analyses provide a solid base for future interstellar searches of deuterated ethylene glycol, enhancing our understanding of the evolution of COMs in the interstellar medium.

Rotational spectroscopy and astronomical search of the HCCSO radical

2025-04-29

C. Cabezas , M. Agúndez , N. Marcelino +2 more

Abstract The number of sulfur-bearing species detected to date in the interstellar medium (ISM) is small compared to oxygen- and nitrogen-bearing species. In fact, the chemistry of sulfur-bearing molecules is … Abstract The number of sulfur-bearing species detected to date in the interstellar medium (ISM) is small compared to oxygen- and nitrogen-bearing species. In fact, the chemistry of sulfur-bearing molecules is strongly dependent on the depletion of sulfur. One of the main inputs to understand the chemistry of sulfur in the ISM is to unveil new molecules containing this element as well as to understand their formation paths. For this purpose, we investigate the rotational spectrum of the HCCSO radical, which seems to be a potential candidate for observation in the molecular clouds where the simpler analog, HSO, has already been detected. The HCCSO radical has been produced by an electric discharge of thionyl chloride (Cl2SO) and acetylene (HCCH) in argon, and its rotational spectrum between 11 and 40 GHz has been characterized using a Balle-Flygare narrow band-type Fourier-transform microwave spectrometer. Accurate spectroscopic parameters were derived from the spectral analysis that were employed to obtain reliable frequency predictions for astronomical searches in different sources. We searched for HCCSO in several molecular clouds where HSO has been observed, B1-b, L183, L483 and TMC-1, but did not detect it. The upper limits to its abundance in these sources were derived.

Accurate rovibrational spectroscopy of relevant astrochemical complexes: CH4⋯CH4, CH4⋯N2 and CH4⋯Ar

2025-04-28

Cassius Carvalho , Ricardo Gargano , João B. L. Martins +1 more

Laboratory Rotational Spectra of Cyanocyclohexane and Its Siblings (1- and 4-Cyanocyclohexene) Using a Compact CP-FTMW Spectrometer for Interstellar Detection

2025-04-24

Gabi Wenzel , Martin Holdren , D. Archie Stewart +4 more

Chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is a versatile technique to record broadband gas-phase rotational spectra, enabling detailed investigations of molecular structure, dynamics, and hyperfine interactions. Here, we present the … Chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is a versatile technique to record broadband gas-phase rotational spectra, enabling detailed investigations of molecular structure, dynamics, and hyperfine interactions. Here, we present the development and application of a CP-FTMW spectrometer operating in the 6.5-18 GHz frequency range, studying cyanocyclohexane, 1-cyanocyclohexene, and 4-cyanocyclohexene using a heated pulsed supersonic expansion source. The dynamic range, experimental resolution, and high sensitivity enable observation of multiple conformers, precise measurements of hyperfine splitting arising from nuclear quadrupole coupling due to the nitrogen atom in the cyano group, as well as the observation of singly 13C- and 15N-substituted isotopic isomers in natural abundance. Using the latter, precise structures for the molecules are derived. The accurate rotational spectra enabled a search for these species toward the dark, cold molecular cloud TMC-1; no signals are found, and we discuss the implications of derived upper limits on the interstellar chemistry of the cyanocyclohexane family.

Gas-phase 2-hydroxypyridine/2-pyridone system: temperature dependence of fractions retrieved from electron diffraction data

2025-04-23

Yuri V. Soldatkin , Anatolii N. Rykov , Ilya I. Marochkin +3 more

Formation of the glycine isomer glycolamide (NH_2C(O)CH_2OH) on the surfaces of interstellar ice grains: Insights from atomistic simulations

2025-04-23

Jessica Perrero , Silvia Alessandrini , Haoyang Ye +2 more

Syn -glycolamide, a glycine isomer, has recently been detected in the G+0.693-0.027 molecular cloud. Investigations into its formation in the interstellar medium could offer insights into synthetic routes leading to … Syn -glycolamide, a glycine isomer, has recently been detected in the G+0.693-0.027 molecular cloud. Investigations into its formation in the interstellar medium could offer insights into synthetic routes leading to glycine in prebiotic environments. Quantum chemical simulations on gly-col-amide ( NH2-C(O)-CH2-OH ) formation on interstellar ice mantles, mimicked by a water ice cluster model, are presented. In this paper, we modeled glycolamide synthesis considering a stepwise process: the coupling between formaldehyde ( H2CO ) and the radical of formamide ( NH2CO^. ) occurs first, forming the glycolamide precursor NH2C(=O)CH2O^. which is then hydrogenated to give anti -glycolamide. We hypothesize that anti -to- syn interconversion occurs in conjunction with glycolamide desorption from the ice surface. The reaction barrier for NH2-C(O)-CH2O^. formation varies from 9 to 26 kJ mol^-1, depending on surface binding sites. Kinetic studies indicate that this reaction step is feasible in environments with a T > 35 K until desorption of the reactants. The hydrogenation step leading to anti -glycolamide presents almost no energy barrier due to the easy H atom diffusion toward the NH2C(O)CH2O^. intermediate. However, it competes with the extraction of an H atom from the formyl group of NH2C(O)CH2O^. which leads to formyl formamide NH2C(O)CHO and H2 . Nonetheless, according to our results anti -glycolamide formation is predicted to be the most favored reactive channel.

Global Reaction Route Mapping of C3H2O: Isomerization Pathways, Dissociation Channels, and Bimolecular Reaction with a Water Molecule

2025-04-18

Dapeng Zhang , Naoki Kishimoto

A comprehensive theoretical investigation of the C3H2O potential energy surface (PES) was conducted, revealing 30 equilibrium structures (EQs), 128 transition state structures (TSs), and 35 direct dissociation channels (DCs), establishing … A comprehensive theoretical investigation of the C3H2O potential energy surface (PES) was conducted, revealing 30 equilibrium structures (EQs), 128 transition state structures (TSs), and 35 direct dissociation channels (DCs), establishing a global reaction network comprising 101 isomerization pathways and dissociation channels. Particular focus was placed on the five most stable isomers, H2CCCO (EQ3), OC(H)CCH (EQ7), H-c-CC(O)C-H (EQ0), HCC(H)CO (EQ1), and HO-c-CCC-H (EQ12), and their reactions with water molecules. Multicomponent artificial force-induced reaction (MC-AFIR) calculations were employed to study bimolecular collisions between H2O and these stable isomers. The product distributions revealed isomer-specific reactivity patterns: EQ3 and EQ7 predominantly formed neutral species at high collision energies, EQ0 produced both ionic and neutral species, while EQ1 and EQ12 exhibited more accessible reaction pathways at lower collision energies with a propensity for spontaneous isomerization. Born-Oppenheimer Molecular Dynamics (BOMD) simulations complemented these findings, suggesting several viable products emerge from reactions with water molecules, including HCCC(OH)2H (EQ7 + H2O), OCCHCH2OH (EQ1 + H2O), and HO-c-CC(H)C(OH)-H (EQ12 + H2O). This investigation elucidates the intrinsic relationships between isomers and their potential products, formed through biomolecular collisions with water molecules, establishing a fundamental framework for future conformational and reactivity studies of the C3H2O family.

Reactivity of syn-CH3CHOO with H2O enhanced through a roaming mechanism in the entrance channel

2025-04-16

Yiqiang Liu , Lijie Liu , Yanlin Fu +7 more

Quantum Tunneling Fingerprints of Chirality-Induced Symmetry Preferences in Methyl Lactate Dimer

2025-04-16

Jiarui Ma , Aran Insausti , Wolfgang Jäger +1 more

Methyl lactate, a chiral molecule with multiple functional groups, has played a pivotal role in advancing experimental and theoretical chiroptical methods. Leveraging conformer-specific jet-cooled rotational spectroscopy in tandem with extensive … Methyl lactate, a chiral molecule with multiple functional groups, has played a pivotal role in advancing experimental and theoretical chiroptical methods. Leveraging conformer-specific jet-cooled rotational spectroscopy in tandem with extensive conformational searches and quantum chemical calculations, we investigated chirality self-recognition in the methyl lactate dimer. The experimental fingerprint-like spectral patterns, including methyl rotor tunneling splittings, allowed the definite identification of one heterochiral and two homochiral binary conformers from a large number of low-energy candidates. Nuclear spin statistics analyses and methyl internal rotor parameters reveal different nuclear tunneling dynamics in the homochiral versus heterochiral environments and highlight the associated chirality-driven symmetry preference in the observed conformers. The results provide comprehensive experimental data for benchmarking quantum chemical calculations of chiral properties and pave the way for the exploration of this prototypical dimer across different frequency ranges using other spectroscopic tools.