Renner–Teller effect

The Renner-Teller effect is a phenomenon in molecular physics and spectroscopy that occurs in polyatomic molecules with degenerate electronic states. It is a blending of the Renner effect and the Teller effect, which describe how molecular vibrations and electronic states interact, leading to splitting of energy levels. Specifically, the Renner-Teller effect is most notable in systems where the degeneracy of electronic states is lifted due to coupling between electronic and vibrational states.