A CI pseudopotential‐based description of the low‐lying states of A_g O₂

Abstract

Extensive SCF-LCAO-MO variational and perturbative configuration interaction (a) calculations framed within an effective core potential approximation have been performed to determine the two experimentally observed geometrical isomers of A g o z and the interconversion route between them. These structural forms, associated to the ground-state local minima, yield virtually the same energy, and their spontaneous interconversion is strongly indicated, which agrees fairly well with the experimental measurements. The reaction A, + Oz + Agoz was theoretically analyzed along a CI fully optimized energy pathway for the ground and various excited states, within Cz. and C, symmetry. Although a tight-ion pair (A: 0;) character is predicted for the ground state at the equilibrium geometries, its dissociation leads to neutral rather than to ionic fragments. The study of the reaction path within C, symmetry shows an avoided crossing between the ground state and another ' A" potential curve where the former correlates adiabatically with the reactants A,('S) + 02('Ag). This indicates that the formation of the complex proceeds via a reactive state of molecular oxygen. The higher ' A" electronic curves correlate with the metal ' P excited state, and the oxygen binding is found to be less favorable. The present results are shown to have an important bearing on the experimentally known catalytic properties of oxygen adsorbed on silver surfaces.