The optical absorption spectrum of the octahedral RhCl63− complex: Ab initio calculations of excitation energies and the effect of spin-orbit coupling

Abstract

The spin-orbit states of octahedral RhCl 6 3− in the three lattices NaCl, Cs 2 NaYCl 6 and water solution have been investigated theoretically with multiconfigurational self-consistent field (SCF) type procedure (CASSCF), followed by a second order perturbation correlation treatment (CASPT2). The spin-orbit effects for the ground state 1 A 1g and the lowest excited states 3 T 1g , 3 T 2g , 1 T 1g and 1 T 2g were calculated with an effective one-electron operator and shifts of more than 1000 cm −1 were found. Different basis sets were tried: the presence of f functions on Rh and d functions on Cl is important for both excitation energies and equilibrium distances. There is agreement between computed excitation energies and the available experimental data that indicate a redshift of the 1 T 1g,2g ← 1 A 1g transitions as the Rh–Cl distance increases.