Collision dynamics of three interacting atoms: Energy transfer and dissociation in collinear motions

The general theory of collisions in three-body systems is applied to vibrational excitation and dissociation in atom--diatom collisions. A multiple collision expansion is introduced for high relative energies, concentrating on single- and double-collision contributions. The general formalism is illustrated with calculations in collinear models for the H+D2 system. They include results for hard-core and exponentially repulsive interactions, and for harmonic oscillator and Morse diatomic potentials. Excitation probabilities are given within the single collision approximation with and without a peaking factorization. Comparison with exact results show that these assumptions are generally valid above threshold energies. For the case of collisional dissociation it is found that double collision events, describing the final channel distortion in the diatomic breakup, are essential to properly cover the energy transfer region between breakup and excitation. Results for dissociation of vibrational excited diatomics show the important role played by initial diatomic momentum distributions and more specifically, by the dynamical form factors of the theory