Jahn–Teller effect in the Γ 8 ( 2 T 2g , t32g) state of ReBr2–6

The Γ8,Γ7(2T2g, t32g)→Γ8(4A2g, t32g) luminescence spectrum of the ReBr2–6 ion in several cubic host lattices has been measured at temperatures down to 6 K. For both transitions the luminescence may be analysed into progressions in the α1g and εg stretching vibrations of the complex ion based on the 2τ1u and τ2u vibronic origins, but the progressions in the τg mode are two orders of magnitude stronger in the T8→ T8 transition than in the Γ7→Γ8 transition. This is strong evidence for a Jahn–Teller effect in the Γ8(2T2g) state of ReBr2–6.