The optical absorption spectrum of the octahedral RhCl3-6 complex:: Ab initio calculations of excitation energies and the effect of spin-orbit coupling

The spin-orbit states of octahedral RhCl63- in the three lattices NaCl, Cs2NaYCl6 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 T-3(1g), T-3(2g), T-1(1g) and T-1(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 off 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 T-1(1g,2g) <-- (1)A(1g) transitions as the Rh-Cl distance increases. (C) 1998 American Institute of Physics. [S0021-9606(98)30532-2]