The E⊗(ε+ε) Jahn-Teller effect

The interaction of an electronic E-term and two degenerate normal vibrations of the same symmetry, leading to the so-called two-mode E⊗(ε + ε) Jahn-Teller effect, is investigated. Absorption spectra are calculated numerically via the Lanczos algorithm and are shown to exhibit new interesting structures. These two-mode spectra are seen to differ markedly from the spectra obtained by simply convoluting the constituting one-mode E⊗ε Jahn-Teller spectra. To classify the spectra we introduce, in addition to the coupling strengths of the individual normal vibrations, a hopping parameter which serves as a measure for the interaction of the normal vibrations via the electronic state. An effective one-mode E⊗ε Jahn-Teller hamiltonian is introduced which reproduces the envelope of the two-mode Jahn-Teller spectrum to a high accuracy.