A classical model for stochastic multiphoton absorption processes of anharmonic molecules

Classical power absorption of an anharmonic molecule in intense infrared radiation is calculated. A generalized damping factor and an effective random phase are introduced for the stochastic field-molecule interaction. It is shown that the over-all broadening of the power response has a fundamental lorentzian, no matter what the source of line broadening is. Excellent agreement with the quantum-mechanical results is obtained by quantizing the classical model.