IR-induced interconversions between five conformers of methanol dimers trapped in nitrogen matrix

Interconversions between five open-chain conformers of methanol dimer trapped in solid nitrogen have been studied through selective excitation of their CH and OH stretching modes. A nearly complete vibrational assignment for three of them is deduced from these irradiation effects and also from thermal conversion observed between 7 and 8 K. Kinetic studies allow us to precise the schemes of conversion and, in favourable cases, to get the quantum yields which are significantly mode dependent. A careful examination of the CO stretching overtone region, around 2050 cm(-1), led to the identification of a simultaneous transition of the CO stretching mode of both molecules, with intensities strongly varying according to the conformer. Such a variation is accounted for in the framework of the theory of the intensities of combination transitions, assuming a dipole-dipole interaction between the two CO bonds. (C) 1997 Elsevier Science B.V.