Diatomics-in-molecules models for H2O and H2O−. I. Valence bond diatomic fragment matrices

Abstract

Valence bond wave functions for the ground states OH(X 2Π) and OH−(X 2Σ+) were analyzed in order to arrive at DIM models for those states of H2O and H2O− correlating with the ground states of the separated atoms. The models are meant to provide a framework for studying the negative ion reaction O−+H2 → OH−+H and to test the utility of DIM in describing at a simple level the bonding in the water molecule. Projection analysis of the ab initio wave functions shows that in addition to the VB structures arising from the coupling of ground state atoms, ionic structures are important, especially for H2O, but that structures with excited states of H can be neglected. Within the space of the DIM model basis functions, diatomic fragment matrices were computed by the VB method to produce library files for eight state manifolds of OH−, six manifolds of OH, two manifolds of OH−−, and four manifolds of H−2. These will be useful as input for future DIM calculations on molecules containing O–H bonds.