Fine structure of the close-lyingA2Π andB2Σ+states of BaH and BaD

Abstract

Molecular parameters for the close-lying and strongly interacting A 2Π and B 2Σ states of BaH and BaD have been re-evaluated by means of a numerical matrix diagonalization procedure. The results obtained according to this exact method deviate considerably from the effective ones of previous investigations, particularly with respect to the A 2Π-B 2Σ+ interaction matrix elements which describe the large Λ-doubling and spin-splitting. The new values of the Λ-doubling and spin-splitting parameters are in excellent agreement with pure precession values for L = 2, and thus the present results form an interesting extension of the pure precession model which so far has been found applicable in a number of cases for which L equals one. The pure precession result L = 2 indicates that the outermost electron of the A 2Π and B 2Σ+ states must be a d-electron, and this requires a re-assignment of the configuration quantum numbers of these states. Strong local perturbations are observed in the rotational levels of the A 2Π state of both BaH and BaD, and the result L = 2 now yields a further confirmation of the previous assumption that a 2Δ state causes these perturbations. In the case of BaD the electronic + vibrational energy and the rotational constants (Bv , Dv ) of the perturbing level could be determined from the perturbed A 2Π term values, and in particular the value of the interaction matrix element leads to the conclusion that there is a A 2Π, v = 0 - 2Δ, v = 2 interaction. Finally the influence of the A 2Π - 2Δ, Δv = 0 interaction on the A 2Π and B 2Σ+ molecular parameters was investigated.