Potential energy surfaces and vibrational energy levels of DCCl and HCCl in three low-lying states

Abstract

We present ab initio multireference configuration interaction (MRCI) calculations for the potential energy surfaces of HCCl in its three low-lying electronic states ( and ), and for the spin–orbit coupling between the and states. The two singlet states become a degenerate 1Δ state in collinear geometries. The potential energy surfaces are interpolated from 6075 MRCI energy points. The final surfaces are slightly adjusted using a coordinate and energy scaling approach. The resulting T e value is 2122.0 cm−1 for and 12209.8 cm−1 for . Vibrational energy levels of DCCl and HCCl are computed for the three states taking into account the Renner–Teller effect and the spin–orbit coupling. The calculated vibronic energy levels are in good agreement with the available experimental values. It is found that the spin–orbit effect is pronounced in the and states.