ROTATIONAL-ISOMERISM OF ETHANOL AND MATRIX-ISOLATION INFRARED-SPECTROSCOPY

The vibrational spectrum of ethanol monomer trapped in argon and nitro gen matrices has been recorded in various conditions of temperature an d irradiation. The structures and vibrational properties of the anti a nd gauche conformers have been investigated by ab initio calculations according to the DFT method. The comparison between observed and calcu lated frequencies allows an explanation of the matrix data and a propo sal of a complete assignment for both conformers. The striking spectra l changes observed in nitrogen matrices upon temperature cycling in th e range 8-30 K are interpreted in term of anti --> gauche conversion. In contrast with these observations, the spectrum obtained in an argon matrix is unsensitive to thermal effects, the anti form being the onl y one to be stabilized. Monochromatic irradiations in the OH and CO st retching regions were carried out with the purpose of inducing photoro tamerization. In all cases only changes of trapping sites were observe d, despite an interconversion barrier lower than the energy of the abs orbed photons.