Kramers-Type Splitting in the X2Π and a4Σ− States of CH and CD Calculated in a Hund's Case (a) Basis

Abstract

We present relativistic ab initio calculations of spectroscopic parameters and rotational term energies of the CH and CD molecules. Potential energy curves have been obtained for a scalar relativistic no-pair Hamiltonian using a multireference configuration interaction (MRCI) approach. Rovibronic couplings have been computed for the ground and first excited states X2Π and a4Σ−. These have been determined through perturbation theory based upon vibronic CI wavefunctions. All important angular momentum couplings including spin–orbit interaction are accounted for, which leads to a correct description of intermediate states between Hund's cases (a) and (b). Experimental values are reproduced very well, and we give some predictions for excited states.