Temperature Dependences of ⁶A_1g → ⁴A_1g, ⁴E_g(⁴G) and ⁶A_1g → ⁴E_g(⁴D) Absorption Bands in RbMnF₃ in Paramagnetic State

The temperature behaviour of RbMnF₃ absorption spectra at T > T_N in the region of the transitions ⁶A_1g → ⁴A_1g, ⁴E_g(⁴G), and ⁶A_1g → ⁴E_g(⁴D) is investigated. Pair–vibronic absorption bands are identified and it is shown that 1. the structure of the spectra in the region of both transitions is caused by the transitions to the ⁴E_g states, 2. the replicas of the basic lines are caused by excitation of an even number of quanta of odd vibrations, and 3. the theoretical temperature dependence of the intensity of the pair–vibronic absorption describes the experimental results sufficiently well.