Theoretical investigation of the Renner-Teller effect in Δ electronic states of tetra-atomic molecules. 2. Perturbative calculation of the vibronic spectrum in the 1¹Δ_g state of B₂H₂ from the linear molecule standpoint

Abstract

Second-order perturbative formulae for handling the Renner-Teller effect in Δ electronic states of symmetric tetra-atomic molecules with linear equilibrium geometry are derived. They are applied to calculate vibronic energy levels of the 1¹Δ_g state of B₂H₂. Perturbative parameters are derived by fitting the ab initio computed potential energy surfaces. The results of the calculations are compared with those obtained by means of a variational approach.