Effects of the interactions between dissociative states and control of the product branching ratios in predissociation

Abstract

The influence of the interactions between the dissociative states on the product branching ratios in predissociation is theoretically analyzed. We adopt the OH molecule as a model system and treat indirect dissociation processes with quantum interferences from the direct dissociation pathways eliminated. Various hypothetical coupling schemes between the bound electronic state and the dissociative states, and those among the dissociative states are employed. When a single dissociative state is involved in the dissociation with no interactions among the asymptotically degenerate states, recoil limit branching ratios of the triplet oxygen fine structure components O(3Pj, j=0,1,2) are attained at all energies. When a dissociative state, coupled with the bound state, is allowed to interact with other dissociative states correlating to the same atomic term, the product branching ratios approach recoil limit values only at a high energy limit. Predissociation through more than one dissociative state, interacting with each other, results in branching ratios that highly depend on the vibrational and angular momentum quantum numbers of the bound electronic state at energies below the dissociation limit to O(1D). Above the threshold to O(1D), the interactions between the dissociation channels give rise to highly oscillating branching ratios as a function of excitation energy. These findings are discussed in connection with the recent experiment of Gordon and co-workers [J. Chem. Phys. 103, 6811 (1995)] on the spin–orbit control in the predissociation of HCl.