Resonances and bound rovibrational levels in the interacting X, A, C, and D states of HeH, HeD, 3HeH, and 3HeD

Abstract

Potential energy curves are calculated for the ten lowest states in HeH which correlate with the hydrogen asymptote in the n=1, 2, 3 occupation; these are X, A, C, D, 5 2Σ+, 6 2Σ+, and B, E, 3 2Π as well as the 1 2Δ states. Multireference configuration interaction calculations are employed thereby in an atomic orbital (AO) basis of contracted Gaussians. Extensive calculations of the ∂/∂R, ∂2/∂R2, Lx, and L2 matrix elements are carried out to account explicitly for the effects beyond the Born–Oppenheimer approximation. The positions of rovibrational levels are thereby determined in pairwise close-coupling calculations for the X/A and C/D states of 2Σ+ symmetry for the four isotopomers 4HeH, 3HeH, 4HeD, and 3HeD. Radial, angular, and mass polarization corrections affect the A and C states differently, so that the A–C energy gap increases by 39 cm−1 in 3HeD and by 53 cm−1 in HeH upon introduction of these terms, e.g., whereby the contribution of the mass polarization is by far the smallest. By employing a two-parameter correction function to the calculated electronic potential energy and making use of the calculated non-Born–Oppenheimer terms, a large number of levels for the A, C, and D states as a function of (v,J) quantum numbers are computed which agree with those, which are experimentally available for the C–A and D–A transitions within wave number accuracy.