Nonadiabatic effects in the B, C, and E, F states of HD

Abstract

The breakdown of the Born-Oppenheimer (B-0) theory gives rise to interactions among the B,C, and E,F states in HD. These so-called nonadiabatic interactions are responsible for the A-doubling of the doubly degenerate C state and also cause intensity perturbations in the transitions from the ground state to these three states. In particular, it is shown that the E,F - X transition which is forbidden in the B-0 theory becomes allowed as a result of nonadiabatic interactions between the B,C, and E,F states. The nonadiabatic energies are calculated by diagonalizing the total HD hamiltonian in a finite basis of adiabatic states. The radial electronic coupling matrix elements arising from the B-E,F interaction are given special consideration. Two different methods for the evaluation of these are discussed. The A-doubling of the C state is calculated for J = 1 to J = 5 and compared to experiment. The overall agreement is very good. The rotational line strengths for transitions from the ground state to the three interacting states are calculated. The nonadiabatic interactions are shown to have a pronounced effect on the rotational line strengths of almost all the levels of these states. The results obtained for the E,F state are significantly different from zero, the value predicted by the B-Q theory.