Vibronically induced Jahn–Teller progressions in the electronic spectrum of iridium hexafluoride

Abstract

The absorption of IrF6 vapor between 0.7 and 1.3 μ consists of three distinct electronic transitions connecting the Γ8g ground state with higher Γ6g, Γ8g, and Γ7g states of the (5d f2g)3 configuration. In first approximation, Jahn–Teller forces vanish in the two Γ8g states, while the Γ6g and Γ7g states involve Kramers magnetic degeneracy, which cannot be split by electrostatic forces. Accordingly, no splittings of the ν2(eg) or ν5(f2g) excited states are observed in these spectra, but short progressions in ν5 do appear in the electric-dipole-allowed, vibronic parts of these transitions. These progressions are considered to show that Jahn–Teller anharmonicity can be induced by admixtures of odd-parity, orbitally degenerate electronic states, i.e. by the same mechanism through which these transitions derive their electric-dipole intensity.