  We summarize a few proposals for mixing F center states through the mediation
of an appropriate symmetry-breaking vibrational mode. Electron-mode coupling
energies odd-order in the mode coordinates are characteristic of the
pseudo-Jahn-Teller mixing of nearly-degenerate opposite-parity electronic
states mediated by an odd-parity vibrational mode. Coupling energies even order
in the vibrational coordinates lead to a pseudo-Renner mixing of even parity
nearly-degenerate states or to dynamic-Renner mixing of degenerate states of
whatever symmetry. Both Renner mixing energies add up to widen the crossover
splitting of the adiabatic energies thereby enhancing the nonradiative
deexcitation rate.
