Effects of orbital angular momentum in PH_2 and PD_2: Renner-Teller and spin-orbit coupling

Abstract

The vibrational and K-type rotational levels of the X˜2B1 and Ã2A1 states of PH2 have been fitted by least squares to give a pair of Born–Oppenheimer potential curves for the combining electronic states. The effects of the orbital angular-momentum coupling between these states, which are derived from a common 2Π state of linear PH2, have been considered in detail. The effects are manifest in both the behavior of the vibronic origins and the effective vibronic spin–orbit coupling constants. We have also calculated the rotational constants for a range of vibronic states of PH2. Analogous rotational constants, band origins, and spin–orbit coupling constants of PD2 have been calculated by use of the potential curves derived from the fit to PH2. The agreement between the calculated origins and those measured experimentally is quite satisfactory. The vibronic dependence of the relative transition moments and of the fluorescence lifetimes have also been calculated for both PH2 and PD2.