NONADIABATIC COUPLINGS AND INCIPIENCE OF QUANTUM CHAOS

The quantization of the electronic two site system interacting with a vibration is considered by using as the integrable reference system th e decoupled oscillators resulting from the adiabatic approximation. A specific Bloch projection method is applied which demonstrates how bes ides some regular regions in the fine structure of the spectrum and th e associated eigenvectors irregularities appear when passing from the low to the high coupling case. At the same time even for strong coupli ng some of the regular structure of the spectrum rooted in the adiabat ic potentials is kept intact justifying the classification of this sit uation as incipience of quantum chaos.