No abstract

The vibrational spectrum of ethanol monomer trapped in argon and nitrogen matrices has been recorded in various conditions of temperature and irradiation. The structures and vibrational properties of the anti and gauche conformers have been investigated by ab initio calculations according to the DFT method. The comparison between observed and calculated frequencies allows an explanation of the matrix data and a proposal of a complete assignment for both conformers. The striking spectral changes observed in nitrogen matrices upon temperature cycling in the 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 only one to be stabilized. Monochromatic irradiations in the OH and CO stretching regions were carried out with the purpose of inducing photorotamerization. In all cases only changes of trapping sites were observed, despite an interconversion barrier lower than the energy of the absorbed photons.

The infrared spectrum of the CH3OH:H2O complex isolated in a nitrogen matrix is here reported. The complex is identified through observation of all three internal modes of the water moiety and 10 out of 12 vibrations of the methanol subunit. Several conformers of the CH3OH...OH2 are evidenced through ir photochemical and thermal conversion process, but none corresponds to the reverse CH3HO...HOH structure, with water playing the role of the proton donor. Ab initio calculations on both structures have been performed to obtain their equilibrium geometries and vibrational spectra. They allow to account for the ir spectral changes (frequencies as well as intensities) of the two submolecules interacting through hydrogen bonding within the complex.