The H2O2+ potential energy surfaces dissociating into H+/OH+: Theoretical analysis of the isotopic effect

We present a detailed study of the potential energy surfaces of the water dication correlating asymptotically with O(P-3) and O(D-1). Using ab initio multireference configuration interaction method, we computed a large ensemble of data, which was used to generate a fit of each potential energy surface for bending angles theta >= 80 degrees degrees and OH distances R-OH >= 1.0 a.u. The fit is used to investigate the dissociation dynamics along each potential energy surface for several initial geometries corresponding to Franck-Condon transition from neutral or singly ionized water molecule. For each case, we determine the dissociation channels and we compute the kinetic energy release and angular momentum distribution of the final arrangements. Among the eight potential energy surfaces investigated here, only the lowest triplet and the three lowest singlet can lead to the formation of bound residual fragment. The dissociation of HOD2+ presents a strong preference for OH rather than OD bond breakage. It is characterized by the isotopic ratio, defined as the number of OD+ over the number of OH+ residual fragments. This ratio depends strongly on the shape of each potential energy surface and on the initial conditions. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3157164]