Renner-Teller effect in six-atomic molecules: Ab initio investigation of the vibronic spectrum of C6-

In this study we introduce a model for handling the Renner-Teller effect in Π electronic states of six-atomic molecules with linear equilibrium geometry. The applied model Hamiltonian excludes the stretching vibrations and end-over-end rotations. On the other hand, it considers the interplay between the vibronic and spin-orbit couplings. We derive perturbative formulae for important coupling cases and apply them to compute the structure of the vibronic spectrum of the X 2Πu state of the C6- ion. The corresponding potential energy surfaces are computed by means of a DFT approach, and the spin-orbit coupling constant by the SA-CASSCF + MRCI method