INTRACONFIGURATIONAL ABSORPTION SPECTROSCOPY OF $IrX_{6}{^{2-}}$ IN $A_{2}MX_{6}$ - TYPE HOST CRYSTALS

Address of Yoo and Keiderling: Department of Chemistry, University of Illinois at Chicago, Box 4348, Chicago, Illinois, 60680, USA.Author Institution:Results of near-ir absorption spectra for $Ir^{+4}$in $A_{2}MX_{6} (A=K, Rb, NH_{4}, M=Sn, Pt, X=Cl, Br)$ type host at $2^{\circ}K$ are discussed and compared to earlier work. Our data indicate that the effect of reduced host symmetry is quite small in this $d^{5}$ system and that the spectra of $IrCl_{6}{^{2-}}$ can be interpreted in a manner paralleling previous studies on $Ir^{+4}$ in cubic hosts. The $IrBr_{6}{^{2-}}$ appears to have a somewhat different vibronic pattern. Shifts of zero-phonon origin and the nature of a vibronic progression were analyzed to correlate with host lattice counter-ions. By comparison to luminescence results of Flint and Paulusz, the latter data are proposed to be indicative of a strongly Jahn-Teller active $e{_g}$ mode