Selective multiple-photon absorption by an anharmonic molecule

We discuss a model of selective absorption of infrared radiation by an anharmonic molecular vibrational mode. The effects of the rotational sublevels and of the energy dissipation mechanisms are described phenomenologically. We show that in the context of our model the absorption process is described by coupled nonlinear equations for the complex vibrational amplitude and for the average excitation quantum number. Two distinct dynamic regimes (coherent and adiabatic limit) can be identified depending on the relative magnitude of the rotational relaxation time and of the laser pulse duration.