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

Direct ab initio dynamics calculations on the photoelectron detachment proc esses of H3O- anion have been carried out by using HF/6-311G** full dimensi onal potential energy surface (PES). Total energy and the energy gradient o f 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 compose d of two isomers, H-(H2O) and OH-(H-2) in which H- and OH- anions are solva ted by H2O and H-2 molecules, respectively. The present calculations indica ted that the available energy, yielded by the electron detachment of H-(H2O ), is almost distributed into the relative translational energy between fra gments. On the other hand, the available energy in an OH-(H-2) isomer is Pa rtitioned into both the relative translational mode and internal modes of t he fragments, although the latter energy is minor. The excitation of intern al modes of the products were observed for only the detachment process of t he OH-(H-2) complex. These are due to the fact that the structure of solven t 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. T he mechanism of the electron detachment process of H3O- is discussed on the basis of theoretical results. (C) 2000 Elsevier Science B.V.