First- and second-order vibronic reduction factors for Jahn-Teller systems

Abstract

The cubic Jahn-Teller (JT) system has been investigated extensively previously. However, orbital triplet systems coupled to more than one t-type mode, as will occur for JT ions in real crystals, have received less attention. The current authors have previously derived expressions for symmetry-adapted vibronic states in the JT system using their unitary shift transformation method. These results are now used to calculate the first- and second-order vibronic reduction factors 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 obtained when the coupling to one mode is weak and the other mode is strong are compared to the analogous results for the simpler system with an additional uncoupled mode. Conclusions are drawn as to how first- and second-order reduction factors for the full multi-mode JT system could be formulated using this approach.