Jahn-Teller effect induced by non-degenerate vibrational modes in cumulenes

The theory of the Jahn-Teller effect induced by non-degenerate vibrational modes is briefly discussed and applied to calculate photoelectron spectra of allene and pentatetraene. Good agreement with the observed spectra is obtained. In both cases it is found that the Jahn-Teller effect is caused by the torsional mode and the antisymmetrical CC stretching mode. The Jahn-Teller effect helps to understand the existence of strong vibronic coupling effects in the related molecules ethylene and butatriene, where no Jahn-Teller effect can be present.