ABSTRACT
Vibrational excitations have an important effect on the transport
properties of molecular junctions. Which modes are important
depends strongly on the coupling of the molecule to the leads. In
this chapter we analyze these effects for both strongly and weakly
coupled molecules and give approximate selection rules for the
vibrational modes. For weakly coupledmolecules the low-frequency
modes tend to be dominant. Their relative intensities are deter-
mined by the so-called Franck-Condon factors. For strongly coupled
conjugated molecules, on the other hand, the modes involving
stretching of the π -bonds determine the transport properties. This
chapter shows how to calculate vibrational effects in both regimes
for the full vibrational spectrum of a molecule.
