The multistate vibronic coupling problem

The interaction of several closely lying electronic states through a vibrational mode is discussed. Several examples are studied which show that this interaction may lead to strong nonadiabatic effects not present in a two-state vibronic coupling problem. Special attention is paid to the vibronic coupling problem in a manifold of randomly distributed electronic states with random coupling. A large number of computations have been performed for such randomly determined electronic systems. In spite of the randomness of the energies and coupling constants, the calculated spectra show some joint trends and regularities.