The 12B2, 12B1, 12A1, 12A2, and 32A′(22B2) states of the 1,1-dichloromethene ion studied using multiconfiguration second-order perturbation theory

The 12B2, 12B1, 12A1, 12A2, and 32A′ (22B2) states of the CH 2 Cl 2 + ion were studied using the CASPT2 and CASSCF methods. For the first four states, adiabatic excitation energy (T0) calculations support the experimental energy ordering and the CASPT2 calculations produced accurate T0 values. The CASSCF calculations produced a large imaginary frequency for 22B2 and predicted a Cs(32A′) minimum-energy structure. The CASPT2 calculations indicate that the 32A′ state is 0.22 eV lower in energy than 22B2, and produced a T0 value for 32A′ identical to the experimental value. We suggest that the third band in the PE spectrum is assigned to 32A′. Potential energy curves for Cl-loss dissociation from the 12B2, 12B1, 12A1, and 12A2 states were calculated at the CASPT2//CASSCF level.