Theoretical investigation of the vibronic spectrum in the X(2)Pi(u) electronic state of C(6)(+).

In this study we employ the recently developed model for handling the Renner-Teller effect in Pi electronic states of six-atomic molecules with linear equilibrium geometry to calculate the vibronic spectrum in the X(2)Pi(u) electronic state of the C(6)(+) ion. 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. The parameters determining the shape of the bending potential energy surfaces are computed by means of a Density functional theory, and the spin-orbit coupling constant by the Multireference CI program using state-averaged complete active space self-consistent field (SA-CASSCF) wavefunctions. The results of the present study are expected to motivate and help future experimental investigations on C(6)(+).