Ab initio investigation of the Renner-Teller effect in tetra-atomic molecules

Abstract

A method for theoretical ab initio treatment of the Renner-Teller effect in tetra-atomic molecules is described. It is based on the model developed in 1972 by Petelin and Kiselev, but instead perturbationally, as in the original work, the vibronic problem is solved by a variational approach. The reliability of the approximations on which the model is based is discussed in detail and checked by the explicit ab initio computations carried out at various levels of sophistication. The model is extended to take into account the interplay between the vibronic, spin-orbit and magnetic hyperfine couplings. The results of ab initio investigations of the structure of spectra involving the ground states, X2πu of C2H2+ and B2H2+ are reviewed.