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

Abstract

This paper reports the results of a theoretical study of the nonadiabatic interactions among the B 1 Σ u + , C 1Π u , and E, F 1 Σ g + states of the HD molecule. The required electronic matrix elements were computed from configuration-interaction wavefunctions. The radial coupling between the B and E, F states, which involves the ∂ ∂R operator, was treated both by numerical differentiation procedures and also by transforming away the ∂ ∂R operator through use of the Hellmann-Feynman theorem. Good agreement between these two approaches was obtained. The nonadiabatic calculation yields C state Λ-doubling values in good agreement with experiment. We also present relative and absolute rotational line strengths for transitions from the ground state ( V X = 0) to this trio of interacting states. Nonadiabatic effects on these line strengths are large for all three band systems. Of particular interest are the E, F ← X bands, where the dipole transitions are allowed only because of these nonadiabatic couplings. These dipole transitions have been recently observed experimentally by Dabrowski and Herzberg [ Canad. J. Phys., 54, 525 (1976)].