Infrared photoisomerization of the methanol dimer trapped in argon matrix: Monochromatic irradiation experiments and DFT calculations

In a first part we propose an accurate assignment of the vibrational spectra of (CH3OH)(2) and ((CH3OH)-O-18)(2) trapped in argon at 7 K, which differentiates the proton donor (PD) and proton acceptor (PA) molecules of four open chain conformers stable at this temperature. Then we describe the effects of monochromatic irradiations in the OH and CO stretching regions which give rise not only to interconversions between these conformers but also to the appearance of one highly unstable species with a lifetime of about 4 minutes at 7 K. Its structure is discussed in the framework of DFT calculations after having checked the reliability of the method on the stable dimeric form. (C) 1997 Elsevier Science B.V.