Vibrational Spectra of cis and trans Oxalyl Fluoride and Their Site-Selective IR-Induced Rotamerization in an Argon Matrix

Lundell

Journal of Molecular Spectroscopy

et al. 2003

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117

102

Absorption spectra of cis and trans conformers of formic acid (HCOOH) isolated in solid argon are analyzed in the mid-infrared (4000-400 cm À1 ) and near-infrared (7800-4000 cm À1 ) regions. The HCOOH absorption spectrum reveals matrix-site splitting for the trapped molecule. Narrowband tunable infrared radiation is used to pump a suitable vibrational transition of the trans conformer in order to promote site-selectively the conversion to the cis conformer and separate the spectral features of each site group. Several anharmonic resonances are identified for both conformers. The results of anharmonic vibrational ab initio calculations (CC-VSCF) for the trans and cis conformers of formic acid are reported and compared with the experimental spectra.

Section: Mid-ir Regionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Vibrational spectroscopy of cis- and trans-formic acid in solid argon

Lundell

Journal of Molecular Spectroscopy

et al. 2003

Self Cite

117

102

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] In general, it is required that the excitation energy is transferred from the initially excited vibrational mode to the reaction coordinate at energies higher than the reaction barrier. 3 However, it has been recently shown that isomerization of the carboxylic group can take place due to tunneling even when the excess energy is transferred to the reaction coordinate ͑C-O torsion͒ below the reaction barrier.…”

Section: Introductionmentioning

confidence: 99%

Rotational isomerism of acetic acid isolated in rare-gas matrices: Effect of medium and isotopic substitution on IR-induced isomerization quantum yield and cis→trans tunneling rate

Khriachtchev

The Journal of Chemical Physics

et al. 2004

Redistribution of carbonyl stretch mode energy in isolated and solvated N-methylacetamide: Kinetic energy spectral density analyses J. Chem. Phys. 135, 214504 (2011) A general and efficient Monte Carlo method for sampling intramolecular degrees of freedom of branched and cyclic molecules J. Chem. Phys. 135, 134121 (2011) Instanton calculations of tunneling splittings for water dimer and trimer J. Chem. Phys. 135, 124109 (2011) Intramolecular vibrational dynamics in S1 p-fluorotoluene. I. Direct observation of doorway states J. Chem. Phys. 135, 124305 (2011) On the stability of Be3: A benchmark complete active space self-consistent field + averaged quadratic coupled cluster study J. Chem. Phys. 135, 104311 (2011) Additional information on J. Chem. Phys. Rotational isomerization of acetic acid (CH 3 COOH) is studied in Ar, Kr, and Xe matrices. The light-induced trans→cis reaction is promoted using resonant excitation of a number of modes in the 3500-7000 cm Ϫ1 region, and the quantum yields for this process are measured for various acetic acid isotopologues and matrix materials. For excitation of acetic acid at energies above the predicted isomerization energy barrier ͑у4400 cm Ϫ1 ͒, the measured quantum yields are in average 2%-3%, and this is one order of magnitude smaller than the corresponding values known for formic acid ͑HCOOH͒. This difference is interpreted in terms of the presence of the methyl group in acetic acid, which enhances energy relaxation channels competing with the rotational isomerization. This picture is supported by the observed large effect of deuteration of the methyl group on the photoisomerization quantum yield. The trans→cis reaction quantum yields are found to be similar for Ar, Kr, and Xe matrices, suggesting similar energy relaxation processes for this molecule in the various matrices. The IR-induced cis→trans process, studied for acetic acid deuterated in the hydroxyl group, shows reliably larger quantum yields as compared with the trans→cis process. For pumping of acetic acid at energies below the predicted isomerization barrier, the trans→cis reaction quantum yields decrease strongly when the photon energy decreases, and tunneling is the most probable mechanism for this process. For the cis→trans dark reaction, the observed temperature and medium effects indicate the participation of the lattice phonons in the tunneling-induced process.

“…Most of the earlier studies used broadband excitation, which can only be selective to some extent. However, a few examples are known in which narrowband irradiation was involved [10][11][12][13][14][15][16]. The limited number of systematic studies performed using narrowband selective vibrational excitation might be partially attributed to the lack of available tunable IR sources.…”

Section: Introductionmentioning

confidence: 99%

“…Narrowband radiation can be used to pump selectively molecules [e.g. HONO and (FCO) 2 ] isolated in various matrix sites [15,16].…”

Section: Introductionmentioning

confidence: 99%

Infrared-induced conformational interconversion in carboxylic acids isolated in low-temperature rare-gas matrices

Khriachtchev

Vibrational Spectroscopy

et al. 2004

Self Cite

An overview of our recent studies dealing with infrared-induced conformational interconversion of carboxylic acids isolated in rare-gas matrices is presented. Extensive rotational photoisomerization studies have been performed on formic acid, which is the simplest organic acid enabling this kind of processes. Formic acid has two conformers and interconversion between them can be induced by vibrational excitation. As such, it is an ideal model system to study the conformational dynamics of the carboxylic group. Formic acid molecules were found to be isolated in different local environments within the rare-gas matrices, as shown by the site splitting of the vibrational bands. Narrowband tunable infrared (IR) radiation was used to induce site-selective isomerization processes. The induced changes in the IR absorption spectra allowed for a detailed analysis of the vibrational properties of both conformers of formic acid isolated in solid argon. In particular, derived from the intermode coupling constants the local environment was shown to affects the intramolecular potential energy surface. Tunneling is involved in the rotamerization of formic acid, with the tunneling rate being affected by the local environment. Additionally, formic acid exhibits isomer-selective photodissociation where narrowband IR excitation can control the conformer-dependent photodissociation channels. Tunable IR radiation was also used to promote rotamerization in a series of matrix-isolated dicarboxylic acids (ethanedioic, propanedioic, and 2-butenedioic acids) by exciting the first overtone of the O-H stretching mode or a suitable combination mode at similar energies. Efficient isomerization involving rotation around the C-O bond was observed in most cases whereas the internal rotation around the C-C bond was found to be constrained for ethanedioic and (Z)-2-butenedioic acids. #