An excitation model for laser-induced photochemical reactions

A model is developed for laser-induced selective low-level excitation of a molecular species which phenomenologically incorporates coherent resonant energy transfer and collision damping. The molecules are represented as harmonic oscillators, perturbed by resonant and non-resonant collisions and driven by an external monochromatic electromagnetic field (laser). The non-resonant collisions are treated as a thermal bath. The laser field is shown to be able to drive the molecules far from thermal equilibrium, even in the presence of collisions. The resonant exchange rate Omega R renormalizes the resonant condition, whereas the non-resonant collision rate Omega D causes damping.