Ro-vibronic states of the NCS radical in the X (II)-I-2 state

Renner-Teller calculations were performed for the X (2)Pi state of the NCS radical using modified multi-reference configuration interaction (MRCI) thr ee-dimensional potential energy functions (PEFs). For the refinements of th e PEFs, existing experimental data were used. In the variational calculatio ns of the ro-vibronic levels for J(total) less than or equal to 7/2 the ful l anharmonicity and all angular momenta couplings were considered. NCS has about 260 ro-vibronic states (J = P, J less than or equal to 7/2) for energ ies up to 4000 cm(-1). Due to a large spin-orbit constant, small bending wa venumber, presence of strong anharmonic resonances, high density of interac ting states, and strong variation of the spin-orbit coupling with geometry, the Renner-Teller problem is found to be more complex than in other 15 val ence electrons ABC molecules. The standard notation for the linear-linear R enner-Teller case was augmented. It allows a qualitative description of var ious perturbations existing in the ro-vibronic states of NCS. The close lyi ng A (2)Pi and B (2)Sigma(+) states cross near the equilibrium geometry of the B-state and form a conical intersection in bent structures.