Classical dynamics and resonance structures in laser-induced dissociation of a Morse oscillator

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Abstract
We study laser-induced dissociation of a Morse oscillator by an ir field as a prototype of multiphoton excitation and dissociation of molecular systems. The driving field is modeled both by a sinusoidal interaction term and by a sequence of δ impulses. We have found that the latter case yields results which closely resemble those of the former and considerably facilitates the computation and analysis. Primary and a sequence of secondary resonances are found in our classical dynamical study and are analyzed by using Chirikov’s nonlinear resonance theory. We have also calculated the dissociation rate as a function of time, dissociation fractions, and half-lives, all for ensembles of initial states uniformly distributed over regions in the phase space. The half-life as a function of the driving field amplitude follows a scaling law with a critical exponent in close agreement with that predicted for the standard map. This fact and the time-dependent dissociation rate reflect the effects on dynamic flows of the partial barriers formed by cantori.