Renner-Teller effect in five-atomic molecules: Ab initio investigation of the spectrum of C5-

A model for handling the Renner-Teller effect in linear five-atomic molecules is developed. The present study is restricted to Π electronic states considered in the harmonic approximation. 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. Perturbative formulae are derived for some particular coupling cases. They are applied to compute the structure of the vibronic spectrum of the X2Πu state of the C5- ion, as well as to interpret the features of the electronic transition between the ground states of C5- and C5. The corresponding potential energy surfaces are obtained by DFT computations.