Dynamics of ionization processes of methanol dimer: a direct ab initio dynamics study

Direct ab initio dynamics calculations have been applied to the ionization process of methanol dimer (CH3OH)(2). Full dimensional ab initio potential energy surface including all degrees of freedom was used in the dynamics calculation. Total energies and gradients were calculated at each time step. The initial geometrical configurations at time zero were randomly selected from the geometries calculated for the neutral dimer at 10 K. It was found that the ionization of neutral methanol dimer leads directly to a long-lived complex formation (methanol. dimer cation) which is composed of CH3O and CH3OH2+. The proton transfer was completed within 10-100 fs after several vibrations of the proton between the heavy molecules as expressed by CH3O...H+... O(H)CH3. For comparison, the bimolecular collision reaction, CH3OH+ + CH3OH, was studied by the same dynamics calculations. Two reaction channels are concerned with the reaction. In addition to the long-lived complex formation channel, the proton transfer-dissociation channel (CH3OH2+ + CH3O) was open as a product channel. (C) 1999 Elsevier Science B.V. All rights reserved.