Abstract
Low-temperature infrared absorption spectra are obtained for ethanol isolated in an argon matrix at temperatures of 20–45 K range for ratios of the numbers of the molecules being studied to the numbers of matrix atoms of 1:1000 and 1:2000. A preliminary interpretation of the spectra is obtained on the basis of the temperature variations in the spectra and published data. The structure of the ethanol conformers, rotational constants, and internal rotation barriers of the methyl and hydroxyl groups are calculated in the B3LYP/cc-pVQZ approximation. The harmonic and anharmonic IR spectra of the gauche- and trans-conformers are calculated in the same approximation. The force fields of the two conformers and the distributions of the potential energy of the normal vibrations are calculated and compared for a general set of dependent coordinates. Anharmonicity effects are taken into account by introducing spectroscopic masses for the hydrogen atoms when calculating the normal vibrations in the harmonic approximation.
Highlights
Alcohol molecules are of interest to researchers because of their ability to form various cluster structures through the formation of intermolecular hydrogen bonds
Low-temperature FTIR spectra of ethanol isolated in an argon matrix have been obtained for a range of temperatures in the 20–45 K range with concentration ratios of 1:1000 and 1:2000
Calculations of the structure of the gauche- and trans-conformers of ethanol in the B3LYP/ cc-pVQZ approximation have made it possible to reproduce the difference in the energies of the conformers and a number of structural and geometric parameters of the molecules in close agreement with experimental data
Summary
Alcohol molecules are of interest to researchers because of their ability to form various cluster structures through the formation of intermolecular hydrogen bonds. By calculating the structure and IR spectra of the two conformers in the B3LYP/6-311þþG(2p, 2d) approximation and following the kinetics of the spectral transformations under laser irradiation of the sample at frequencies corresponding to the O-H and C-O bonds, he was able to come up with a reliable experimental attribution of the absorption bands in the vibrations of the gauche- and trans-conformers of ethanol. He showed that an argon matrix stabilizes the transconformer, while both conformers are present in a nitrogen matrix and there are no inter-conformer transitions with laser irradiation in the ranges indicated here. Be noted that these calculations were done in the harmonic approximation and that the theoretical description of the normal vibrations is approximate
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