A coupled treatment of 1Σ+ and 3Π states of AgH molecule

Ab initio configuration interaction (CI) calculations have been carried out for the potential curves of the lowest five 1Σ+ and three 3Π electronic states of the AgH molecule. Nonadiabatic couplings among the 1Σ+ states and spin–orbit interaction matrix elements between the 1Σ+ and 3Π states have been evaluated. The resulting adiabatic potential curves and couplings are transformed to a diabatic representation by employing a unitary transform which eliminates all d/dR coupling terms. Energy positions and predissociation rates for vibrational levels associated with the above electronic states are determined by employing a complex scaling approach based on both the adiabatic potential curves and their diabatic counterparts and the associated nonadiabatic couplings. It was found that the differences between these two sets of results for vibrational spacings and predissociation rates are marginal. The calculated spectroscopic constants for the X1Σ+, A1Σ+ and a3Π states are in good agreement with measured results, and the calculated vibrational spacings for the A1Σ+ state are also in reasonably good agreement with experiment. The reasons behind the relatively large discrepancies in the predicted and measured Te values for the c3Π and B1Σ+ states are discussed. Predissociation linewidths are predicted for the vibrational levels of these electronic states. The decay of the A1Σ+ and B1Σ+ states is caused by nonadiabatic effects, whereas that of the a3Π and c3Π states is induced by the spin–orbit interaction.