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Vibronic effects

Vibrational-electronic (vibronic) effects are caused by coupling the electron motion to the oscillatory motion of the atomic nuclei and experimentally examined with the help of electronic spectroscopy, for example. Typical examples of vibronic effects are vibrational transitions that accompany electronic transitions.

In the theoretical description, one starts either from the crude-adiabatic approximation, in which the electronic Schrödinger equation is solved for a clamped nuclear arrangement, or from the Born-Oppenheimer approximation, in which for each arrangement of the nuclei the electronic Schrödinger equation is solved anew. Subsequently, with the resulting potentials from the electronic Schrödinger equation the vibrational Schrödinger equation is solved, taking into account further coupling effects, where appropriate.

We are especially interested in Franck-Condon, Herzberg-Teller and Jahn-Teller effects and their efficient description, because the latter represents a special challenge due to the generally high density of vibrational states. Franck-Condon effects are particularly important for the laser cooling of molecules. Herzberg-Teller-Effects, among other things, give rise to vibronically induced transitions, which are forbidden in the Franck-Condon approximation. And Jahn Teller effects finally occur in degenerate electronic states and lead to a rich structure in vibronic spectra.