  We propose a novel approach to calculate dynamical processes at ultrafast
time scale in molecules in which vibrational and electronic motions are
strongly mixed. The relevant electronic orbitals and their interactions are
described by a Hubbard model, while electron-phonon interaction terms account
for the bond length dependence of the hopping and the change in ionic radii
with valence charge. The latter term plays a crucial role in the non-adiabatic
internal conversion process of the molecule. The time resolved photoelectron
spectra are in good qualitative agreement with experiments.
