  Anharmonicities provide a wealth of information about the vibrational
dynamics, mode coupling and energy transfer within a polyatomic system. In this
contribution we show how driven molecular dynamics trajectories can be used to
extract anharmonicity properties under very short times of a few hundreds of
vibrational periods, using two exciting fields at- and slightly off-resonance.
Detailed analyses on generic quartic potential energy surfaces and applications
to various model systems are presented, giving good agreement with perturbation
theory. Application to a realistic molecule, cubane (C$_8$H$_8$), modeled with
a tight-binding quantum force field, further indicates how the method can be
applied in practical cases.

Chemical Physics