On the Jahn-Teller effect in IrF6: the Γ8g(t2g)3state at 6800 Å

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Abstract
In this work we present a detailed discussion of the highest energy (t 2g )3 transitions of IrF6, Γ8g (2 T 2g )⇃Γ8g (4 A 2g ) at 14 900 cm-1 and Γ7g (2 T 2g ) ⇃ Γ8g (4 A 2g ) at 12 100 cm-1, as observed in dilute mixed crystals with UF6, MoF6, and WF6 at 4·2 and 1·8 K. The system is of particular interest because Γ8g states are Jahn-Teller active and the Γ7g state serves as an excellent example of what may be expected for a similar but non-Jahn-Teller active state. It is found that the usual linear Jahn-Teller interaction involving either v 2(e g ) or v 5(t 2g ) cannot account for the observations of both shifts and splittings of v 5(Γ8g ). In order to explain all the relevant observations, theories encompassing higher-order vibronic coupling terms and/or coupled v 2-v 5 linear effects must be considered. Based on calculations, IrF6 is assigned an approximate D 4 h symmetry in the mixed crystals. A new electronic charge-transfer state (Γ7g or Γ6g ) is located at ∼ 15 900 cm-1 and stretching vibrations n(v 1′, v 2′, v 3′) (n=1, 2) are identified built on this origin.

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