The Jahn-Teller coupling of a triplet state in cubic surroundings to both $E_g$ and $T_{2g}$ modes of vibration can lead to a vibronic ground state that includes both tetragonal and trigonal distortions if the energy difference between the static distortions is small. A simple model is set up to study the properties of this ground state, assuming the Jahn-Teller coupling is strong, so that the adiabatic approximation can be used. Expressions for the reduction factors $K\left(E\right)\mathrm{}$ and $K\left(T_2\right)$, the $g$ values, and their sensitivity to strains in the crystal are derived. These properties interpolate nicely between those appropriate to coupling to $E_g$ or $T_{2g}$ modes separately. The ground state is a triplet belonging to the same irreducible representation as the original triplet throughout the range of parameters considered.

• Received 4 June 1969

DOI:https://doi.org/10.1103/PhysRev.187.407