Hybrid quantum/semiclassical wave packet method for molecular dynamics: Application to photolysis of Ar...HCl

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Abstract
A hybrid quantum/semiclassical method is proposed and applied to study realistically the dynamics of the three-fragment photodissociation process Ar...HCl+hν→Ar+H+Cl. In the method the hydrogen motion is treated by exact quantum mechanics, while the heavy atoms are described by semiclassical Gaussian wave packets. This treatment is expected to reproduce the main quantum features of the dynamics. Part of the wave packet is found to describe resonance events in which the light particle is temporarily trapped inside the Ar...Cl cage and oscillates periodically between the heavy atoms before it dissociates. Interference between frequency components of the H wave function that populate different resonance levels give rise to interesting quantum effects. Such effects appear in the angular distribution of the hydrogen fragment, which shows some diffraction oscillations, and scattering into classically forbidden regions. Quantum interferences between the resonances are also the cause of a pronounced structure of peaks in the H photofragment kinetic energy distribution (KED). Time-correlation functions of the wave functions involved are computed, and the implications for the absorption spectrum and its relation to the KED of the H atom are discussed. The results demonstrate the power and applicability of quantum/semiclassical time-dependent self-consistent-field (TDSCF) as a tool for studying the dynamics and spectroscopy of realistic molecular systems.

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