Perturbative handling of the Renner-Teller effect and spin-orbit coupling in Δ electronic states of triatomic and tetra-atomic molecules

Abstract

Second-order perturbative formulae for handling the Renner-Teller effect combined with the spin-orbit coupling in Δ electronic states of triatomic and symmetric (ABBA-type) tetra-atomic molecules with linear equilibrium geometry are derived via two schemes for partition of the model Hamiltonian. The formulae for triatomic molecules are employed to compute the spectrum of the X5Δg state of FeH2. The parameters entering the model Hamiltonian are generated by means of ab initio calculations. © 2002 Elsevier Science (USA).