Predissociation lifetimes of vibrational levels of the excited 1B1 (K a′=0) electronic states of Cd⋅H2 and Cd⋅D2 complexes

Abstract

The experimental rates of predissociation of vibrational levels of the 1B1 (Ka′=0) excited states of the Cd⋅H2 and Cd⋅D2 complexes are shown to be consistent with both semiclassical and quantum-mechanical pseudodiatomic theoretical treatments of the process. The 1B1 pseudodiatomic potential was constructed by fitting an analytical function to the experimentally estimated Rydberg–Klein–Rees (RKR) inner and outer turning points. The potential of the repulsive 3A1 state was estimated by fitting an exponential function to the ab initio points of Boatz, Gutowski, and Simons, then adjusting the exponential parameter slightly to maximize overall agreement with the observed Cd⋅H2 and Cd⋅D2 predissociation lifetimes. The best-fit repulsive curves for both the semiclassical and quantum-mechanism calculations result in slightly ‘‘outer-wall’’ 1B1/3A1 crossings at only 84 and 76 cm−1, respectively, above the 1B1 potential minimum. The 1B1/3A1 coupling matrix elements derived from both treatments were ∼150–160 cm−1, much smaller than the 404 cm−1 expected if the spin–orbit interaction were unchanged from that of the asymptotic Cd(5s5p) states. It is suggested that the apparent reduction in the coupling strength could be due to the marked change in the nature of the Cd 5pσ orbital due to the strong repulsive interaction with H2 in the 3A1 state and to the neglect of the anisotropy of the 1B1/3A1 triatomic potential surface crossing.