Vibrational spectra of the methanol tetramer in the OH stretch region.Two cyclic isomers and concerted proton tunneling

摘要

Second order M0ller-Plesset perturbation theory and density functional theory are employed t< localize several stationary points on the potential energy surface of the cyclic methanol tetramer Two cyclic isomers are identified: one of S4 symmetry, with methyl groups in up-down-up-dowl configuration, and a second one of C i symmetry , with the methyl groups in up-up-down-dowl configuration. The latter minimum is 360 cm- 1 above the S 4 minimum, with a barrier of 475 cm - separating them. These isomers give rise to fopr asymmetric OH modes around 3300 cm-l. )! model of the concerted proton transfer,S4-+Did-+S4 (Did is th~transition structure), yields aJ estimate of 0.7 cm-l for the tunneling splitting of the totally syinmetric OH stretch vibrationa fundamental. Raman spectra would show evidence of this fundamental and help to identif~ admixtures of the Ci isomer.