Electronic states of the ion studied using multiconfiguration second-order perturbation theory

Abstract

Abstract Electronic states of the CS 2 + ion were studied using the CASSCF and CASPT2 methods in conjunction with an ANO basis. The CASPT2(⧸⧸CASSCF) adiabatic excitation energy ( T 0 ) calculations support the assignments of the X, A, B, and C states of CS 2 + to 1 2 Π g , 1 2 Π u , 1 2 Σ u + , and 1 2 Σ g + , respectively, and indicate that the 2 2 Π u and 3 2 Π u shake-up states lie between 1 2 Π u and 1 2 Σ u + and the 4 2 Π u and 2 2 Π g shake-up states lie between 1 2 Σ u + and 1 2 Σ g + , which seemingly confirms the observation of satellite bands between the A and B bands and between the B and C bands. However the four shake-up states do not represent minima in the potential energy surfaces (PESs). We found minima in the PESs of the 2 2 B 1 , 3 2 B 1 , 3 2 A 1 , 4 2 A 1 , and 2 2 A 2 states, which are the resultant states of Renner splitting in the four shake-up Π states. We attribute satellite band I to 2 2 B 1 , 3 2 B 1 , and 3 2 A 1 , since the CASPT2 T 0 values of the three states are between the CASPT2 T 0 values of A 2 Π u and B 2 Σ u + . We attribute satellite band II to 4 2 A 1 and 2 2 A 2 , since the CASPT2 T 0 values of the two states are between the CASPT2 T 0 values of B 2 Σ u + and C 2 Σ g + .