Direct ab initio dynamics study of the photoelectron detachment processes of the H3O- anion

Direct ab initio dynamics calculations on the photoelectron detachment processes of H3O- anion have been carried out by using HF/6-311G** full dimensional potential energy surface (PES). Total energy and the energy gradient of atoms were calculated in each time step. The excess energy was assumed to be zero at the starting point of the trajectory. The H3O- anion is composed of two isomers, H-(H2O) and OH-(H-2) in which H- and OH- anions are solvated by H2O and H-2 molecules, respectively. The present calculations indicated that the available energy, yielded by the electron detachment of H-(H2O), is almost distributed into the relative translational energy between fragments. On the other hand, the available energy in an OH-(H-2) isomer is Partitioned into both the relative translational mode and internal modes of the fragments, although the latter energy is minor. The excitation of internal modes of the products were observed for only the detachment process of the OH-(H-2) complex. These are due to the fact that the structure of solvent molecules (H2O and H-2) in each complex is significantly close to that of free molecules whereas the PES of the neutral state is always repulsive. The mechanism of the electron detachment process of H3O- is discussed on the basis of theoretical results. (C) 2000 Elsevier Science B.V.