CASPT2 study on electronic states of the C6H5Cl+ ion

Geometries of the 12B1, 12A2, 12B2, 22B1, and 12A1 states of the C6H5Cl+ ion were optimized by using the CASPT2 method in conjunction with a contracted atomic natural orbital basis and the optimized geometries of the 12B2, 22B1, and 12A1 states are significantly different from the previously reported CASSCF optimized geometries. However, the CASPT2 calculations predict the adiabatic excitation energy (T0) ordering of X2B1, 12A2, 12B2, 22B1, and 12A1 as the previous CASPT2//CASSCF calculations. H-loss dissociation processes, C6H5Cl+ → C6H4Cl+ + H, for the five states of the C6H5Cl+ ion were studied at the CASPT2//CASSCF level. Ten electronic states of the C6H4Cl+ ion, as the dissociation product, were studied using the CASPT2 and CASSCF methods. By checking the CASPT2//CASSCF results for the asymptote products along the CASPT2//CASSCF potential energy curves, the X2B1, 12A2, 12B2, 22B1, and 12A1 states of the C6H5Cl+ ion are found to correlate with a3B1, B1A2, A1B1, d3B2, and X1A1 states of the C6H4Cl+ ion, respectively. Appearance potentials for the C6H4Cl+ ion in the five states are predicted.