  Quantum transport through single molecules is essentially affected by
molecular vibrations. We investigate the behavior of the prototype single-level
model with intermediate electron-vibron coupling and arbitrary coupling to the
leads. We have developed a theory which allows to explore this regime via the
nonequilibrium Green function formalism. We show that the nonequilibrium
resonant spectroscopy is able to determine the energies of molecular orbitals
and the spectrum of molecular vibrations. Our results are relevant to scanning
tunneling spectroscopy experiments, and demonstrate the importance of the
systematic and self-consistent investigation of the effects of the vibronic
dynamics onto the transport through single molecules.
