High-resolution IR spectroscopy is confined to the study of atoms and molecules in the gas phase at low pressures, where the interaction energy between particles is orders of magnitude lower than in the condensed phases. The intermolecular interactions broaden the energy levels, and, consequently, the spectral lines, preventing the observation of finer details in the spectra. The main applications covered in this chapter are the accurate determination of rotation and rotation-vibration molecular energies; the determination of the molecular geometry of simple molecules; the evaluation of force field and of the vibration- and rotation-vibration interactions; the measurement of pressure broadening and pressure shift of the spectral lines; the determination of electric dipole moments via laser-Stark spectroscopy; the studies of intramolecular dynamics; the calculation of rate constants, equilibrium constants and other thermodynamic data; the evaluation of relaxation times.

2014 High resolution Fourier transform spectra, recorded between 30 and 460 cm-1, have been used for an extensive analysis of the (n, 03C4) = (0, 3) ~ (n’, 03C4’) = (0, 1), (0,1) ~ (0, 3) and (1, 1) ~ (0, 3) torsionrotation bands of H2O2. Then, using a Hamiltonian which takes explicitly into account the strong | 0394Ka| = 2 interaction between the rotational levels of the (n, 03C4) = (0,1) and (1,1) torsional states, as well as the |0394Ka| = 2 interaction between the (n, 03C4) = (1, 1) and (2, 1) rotational levels, it has been possible to reproduce very satisfactorily the experimental rotational levels of the (n, 03C4) = (0, 1) and (1,1) torsional states and a precise set of torsional energies and rotational and coupling constants has been derived. In the same way, to fit the (n, 03C4) = (0, 3) experimental energy levels we have used a Hamiltonian taking into account the |0394Ka| = 2 interaction between the rotational levels of the (n, 03C4) = (0, 3) and (1, 3) torsional states, and this calculation has also provided a precise set of torsional energies, rotational and coupling constants for the (n, 03C4) = (0, 3) and (1, 3) torsional states. J. Phys. France 49 (1988) 1901-1910 NOVEMBRE 1988, Classification Physics Abstracts 33.20E 35.20J 35.20P

We report results from measurements of the high resolution FTIR spectrum for the fully deuterated benzene molecule C6D6 in the range 450-3500 cm(1). Accurate spectroscopic constants have been obtained for the fundamental vibration nu(11) at 496.208 cm(1) and improved ground state constants have been deduced from a fit of ground state combination differences. The J structure of the combination parallel bands nu(2) + nu(11) (at 2798.1 cm(1)), nu(5) + nu(12) (1802.5 cm(1)) and nu(7) + nu(16) (2619.3 cm(1)) of C6D6 has been analysed as well, from which improved values of the band origin and of the B and DJ constants of the excited states have been obtained. The strongest hot bands accompanying these parallel transitions have been assigned by means of the anharmonic force field calculated by MASLEN et al. [1992, J. chem. Phys., 97, 4233]. In particular (nu(11) + nu(16)) - nu(16) is assigned to the band at 492.4 cm(1) even though its shape is typical of a perpendicular transition (PAPE). New values for the nu(5), nu(12) and nu(16) band origins are determined from the band origins of combination bands and from calculated anharmonic constants. Numerous anharmonic constants are derived from the assignment of hot band and combination transitions.

The harmonic frequencies ωest of 12C6H6 calculated by combining the anharmonic constants from a DFT quartic force field with the experimental fundamentals, are compared with harmonic frequencies, ωcalc, obtained with different theoretical methods. One set of ωcalc was derived by Martin, Taylor and Lee by ab initio CCSD(T) theory, the others have been calculated by us by means of the density funcional theory DFT with B3LYP, B3PW91, B3P86 and mPW1PW hybrid functionals. The mean absolute deviation between ab initio ωcalc and ωest is 6.8 cm−1 while between DFT ωcalc and ωest is between 8.6 and 10.5 cm−1. Moreover the DFT ωcalc show a small systematic underestimation of the CH stretching vibrations.

The anharmonic force field of benzene has been calculated using a finite difference method by means of density functional theory (DFT) with the B3LYP functional and a TZ2P atomic orbitals basis set, and compared to the field calculated by Maslen et al. [J. Chem. Phys. 97, 4233 (1992)]. The vapor phase infrared (IR) spectra of benzene (natural isotopic mixture) and of C12-benzene have been recorded from 450 to 6000 cm−1, at resolutions varying from 0.05 to 0.008 cm−1, and at various path lengths (0.18/42 m). The parallel bands ν11, ν4+ν12, ν5+ν12, ν2+ν11, and ν7+ν16, using the Wilson numbering, with their accompanying hot bands, have been analyzed and their origins determined to test our computed anharmonic force field. The Raman spectra of gas-phase benzene have been also recorded at medium resolution (∼0.7 cm−1) using an argon laser (line at 514.5 nm) with a power of 0.8 W and a multipass cell. In this work we compare the experimental and the theoretical frequencies and band profiles of the parallel ν1, ν2, 2ν16, 2ν4, and 2ν14 and of the corresponding hot bands, taking into account the l-vibrational doubling and all Fermi resonances within 100 cm−1. By comparison with experiment, the DFT B3LYP is shown to be more accurate than the self-consistent field (SCF): the fundamentals are calculated with a mean absolute error of 10.7 cm−1 and most of the spectroscopic constants are in better agreement with the experimental values.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGeometry of Benzene from the Infrared SpectrumElisabetta Cané , Andrea Miani , and Agostino Trombetti View Author Information Università di Bologna, Dipartimento di Chimica Fisica e Inorganicia, Viale Risorgimento 4, 40136 Bologna, ItalyCite this: J. Chem. Educ. 1999, 76, 9, 1288Publication Date (Web):September 1, 1999Publication History Received3 August 2009Published online1 September 1999Published inissue 1 September 1999https://pubs.acs.org/doi/10.1021/ed076p1288https://doi.org/10.1021/ed076p1288research-articleACS PublicationsRequest reuse permissionsArticle Views645Altmetric-Citations5LEARN 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:Aromatic compounds,Chemical structure,Energy levels,Hydrocarbons,Infrared light Get e-Alerts

The IR spectra of phenanthrene-h10 and -d10 have been recorded in the vapour phase from 200 to 3200 cm−1 with a resolution of 0.2 cm−1, using a multipass cell heated at 90°C. The assignment of the vibrational bands has been performed by comparison with the theoretical spectra, evaluated using Density Functional Theory and Scaled Quantum Mechanical (SQM) force fields. We found that both methods reproduce the sequence of the experimental frequencies to a good accuracy, allowing in most cases consistent and unambiguous assignments. The relative intensities have also been measured and compared with theory.

Kinetics of chlorobenzene hydrodechlorination have been measured over Ni on SiO2, Al2O3, MgO, activated carbon and graphite. A stepwise variation of Ea is analysed using the selective energy transfer model where Ea is identified as the vibrational energy associated with an excitation of the chlorobenzene out-of-plane C–H bending mode. Variation of Ea with vibrational quantum number yields a vibrational frequency of 749 cm−1 and a value (−1.1 cm−1) for the anharmonicity term, which is characteristic of bending vibrational modes. Our analysis suggests that the reacting species are weakly adsorbed on the catalyst: heat of adsorption = −0.31 kJ mol−1.

The IR spectra of anthracene-h(10) and -d(10) have been recorded for the first time in the gas phase from 450 to 3200 cm(-1) with a resolution of 0.2 cm(-1), using a multipass cell heated to 100 degrees C. For the assignment of vibrational bands we have evaluated the theoretical spectrum using density functional theory (DFT) and scaled self consistent held force fields. We found that both methods reproduce the sequence of the experimental frequencies to a good accuracy, allowing in most cases consistent and unambiguous assignments. The relative intensities of C14H10 and C14D10 have also been measured and compared to theory. (C) 1997 American Institute of Physics.

The fundamental wavenumbers v(6), v(7), v(8) and v(19) of gas phase benzene have been accurately determined from combination and difference bands present in the infrared spectrum. The anharmonic contribution to the vibrational energy was estimated by means of some anharmonic constants calculated by ab initio methods by Handy et al. [J. Chem. Phys. 97 (1992) 4233]. The fundamentals were checked by comparison with the overtones present in the Raman spectrum determined by Eppinger et al. [J. Mel. Struct. 266 (1992) 389]. (C) 1997 Elsevier Science B.V.

The gas-phase IR spectrum of 1-azaindolizine has been recorded in the range from 100 to 3200 cm(-1), at the resolution of 0.05 cm(-1), using a multipass cell heated to 80 degrees C. The spectrum analysis has been performed by comparing the experimental spectrum with the theoretical one, using both frequency and intensity matching as guidelines for the assignments. The theoretical spectrum of 1-azaindolizine has been calculated from the harmonic force field evaluated at the self consistent field (SCF) level followed by empirical scaling according to the scaled quantum mechanical (SQM) approach, with pyridine and imidazole as parent molecules. The final root-mean-square deviation (RMSD) of the computed and experimental frequencies is 18 cm(-1).

The vapour phase IR spectra of naphthalene-h(8) and -d(8) have been recorded from 450 to 3200 cm(-1), at the resolution of 0.05 cm(-1), using a multipass cell heated to 50 degrees C. Using the new spectral data and taking the frequencies of all Raman active vibrations from the literature we assign all fundamentals. The experimental frequencies are compared to the theoretical ones both computed with the Self Consistent Field method, followed by the Scaled Quantum Mechanical (SQM) method, and by the Density Functional Theory (DFT). The infrared spectrum of naphthalene is reproduced to a good accuracy with both methods leading in most cases to unambiguous assignments. The absolute infrared intensities of some fundamentals of C10H8 and the relative intensities of C10D8 have been measured and compared to those evaluated by SQM and DFT.

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The gas-phase IR spectrum of indazole has been recorded from 100 to 4000 cm–1, using a multipass cell heated to 120 °C, and completely assigned using theoretical predictions based on the scaled quantum mechanical (SQM) method. The single-crystal IR spectrum of this molecule, previously reported, has been compared with our data and partially reassigned. The harmonic force field of indazole, evaluated at the HF-SCF level using 6-31G** orbitals, is corrected by scaling the force field over a convenient set of internal coordinates. Scaling factors were determined by least-squares fitting of the theoretical to the experimental frequencies of two parent molecules, benzene and pyrazole and their perdeuteriated isotopomers. Our final prediction gives frequencies for indazole which, on average, differ from experiment by 24 cm–1. We confirm the validity of the SQM method as a practical tool for a complete analysis of vibrational spectra, even for molecules of this complexity.

The microwave spectra of 1H-benzotriazole and its N-D isotopomer and of 1,2,4-triazolo[1,5-a]pyrimidine have been investigated in a heated cell. Both molecules are planar. Their dipole moments have been measured. The rotational spectra of some vibrational satellites belonging to the butterfly and 1,3-twisting vibrations have also been assigned.

The 000 bands in the S1-S0 electronic absorption systems of lH-benzotriazole at 286 nm and of 1,2,4-triazolo[l,5-a]pyrimidine at 315 nm have been analyzed by computer simulation of their rotational contours. The results have shown that the benzotriazole hand is an almost pure type-B band, while in the case of 1,2,4-triazolo[l,5-a] pyrimidine it is a pure type-A band, so each S1-S0 electronic system is assigned as Ã1A′(ππ*)-X̃1A′. In both of these molecules, the transition moment is in the molecular plane, almost parallel to the b-inertial axis in benzotriazole. while it is parallel to the a-inertial axis in 1,2,4-triazolo[1,5-a]pyrimidine. Since the S1-S0 transitions in the indole derivatives previously analyzed were shown to be π*-π, it seems likely that the nature of the S1-S0 electronic transition is the same in all the molecules of this kind.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The 000 band of the S1-S0 electronic absorption system of indazole at 290 nm has been analyzed, and the results of the computer simulation of its rotational contour have shown that this band is and AB hybrid with an intensity ratio AB = 1.22. The S1-S0 electronic system is assigned as Ã1A′(ππ∗)-X̃1A′. The same result has already been reached for benzimidazole (E. Canéet al., J. Mol. Spectrosc.150, 222–228 (1991)), and other ring-condensed aza-aromatic compounds although the relative amount of the type B and A components is different in each band. The transition moment is in the molecular plane nearly equidistant from the a- and b-inertial axes (θ = ±42°).