A new semiclassical decoupling procedure for rotational projection states in rovibrationally inelastic atom-diatom and diatom-diatom collisions is developed. Computed vibrational self-relaxation rate constants for para-H2 and ortho-H2 are in good quantitative agreement (within a factor of 1.5, except for the lowest temperatures) with experimental data over the investigated temperature range 50–2000 K. This allows us to hope that also more detailed (nonmeasured) rate constants for rovibrational state-to-state transitions in molecular hydrogen, calculated by our new model, are sufficiently accurate for astrophysical applications.
Various quantum decoupling and semiclassical methods are used to calculate cross sections for rotational and rovibrational transitions in O2+ colliding with Kr. A general analysis of time scales for rotational and vibrational excitations and of coupling strengths for the corresponding potentials is used to review the standard decoupling methods that treat separately vibrations and rotations in atom-molecule collisions. When such decoupling is applied to strongly interacting ionic systems and to heavy particles, it is found to fail rather dramatically and to be brought back to reliable values only when fully coupled rovibrational equations are used to treat the dynamics.
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