FIRST-ORDER AND 2ND-ORDER VIBRONIC REDUCTION FACTORS FOR T-CIRCLE-TIMES-2T(2) JAHN-TELLER SYSTEMS

The cubic T x t Jahn-Teller (JT) system has been investigated extensiv ely previously. However, orbital triplet systems coupled to more than one t-type mode, as will occur for JT ions in real crystals, have rece ived less attention. The current authors have previously derived expre ssions for symmetry-adapted vibronic states in the T x 2t(2) JT system using their unitary shift transformation method. These results are no w used to calculate the first- and second-order vibronic reduction fac tors for spin-orbit coupling for this JT system. A discussion is given on whether is appropriate to formulate this problem with two strongly coupled modes in terms of one effective mode. Also, the results obtai ned when the coupling to one mode is weak and the other mode is strong are compared to the analogous results for the simpler T x t system wi th an additional uncoupled mode. Conclusions are drawn as to how first - and second-order reduction factors for the full multi-mode T x nt(2) JT system could be formulated using this approach.