RATE EQUATIONS APPROACH TO THE INFRARED COLLISIONLESS MULTI-PHOTON EXCITATION

It is suggested to assume a spectral structure for the infrared absorption of highly excited molecules. Ascribing to each excited level an absorption cross section σε{lunate} the multiphoton absorption can be treated by rate equations. An analytic solution is presented for some simple but not unrealistic assumptions on σε{lunate}. It agrees quantitatively with absorption and dissociation data on SF6. An Arrhenius-like dependence of the dissociation probability on incident energy flux is predicted, although the level populations are completely nonthermal. The σε{lunate} best fitting the experiments can be interpreted as lorentzians which substantially shift but only slightly broaden with increasing excitation energy. © 1979.