Optical transitions of Rh2+ in NaCl crystals studied by electron spin resonance and magnetic circular dichroism

Electron spin resonance, magnetic circular dichroism, and optical absorption spectra of a paramagnetic Rh2+ complex are investigated in Rh3+ doped solution-grown NaCl single crystals, x irradiation of the crystals at 77 K followed by a warm-up to room temperature results in the formation of a stable low-spin Jahn-Teller distorted RhCl64- complex possessing D-4h symmetry. The unpaired electron is largely localized in the 4d(z2) orbital of the Rh2+(4d(7)) which is involved in a sigma type molecular bond with two symmetrically placed Cl- ions along [001]. The magnetic circular dichroism and optical absorption measurements at 1.4 K reveal two main bands around 12 200 cm(-1) and 16 200 cm(-1). Within the octahedral Tanabe-Sugano formalism of the Rh2+ these two absorptions are associated with two vibronically allowed E-2(g)-->T-2(1g),T-2(2g) molecular transitions. This assignment is in quantitative agreement with the analysis of the g matrix components. A small MCD feature at 15 200 cm(-1) is tentatively associated with two coinciding E-2(g)-->T-2(1g),T-2(2g) transitions of another, probably a ligand-exchanged, Rh2+ center. [S0163-1829(99)00517-2]