Metastable Methane Dimers in Collisions with Inert Gas Atoms: Study According to the Method of Classical Trajectories

The formation of collision complexes, also called quasi-complexes (QCs), metastable dimers, or Feshbach resonances, is studied for CH₄–He, Ne, and Ar systems by the method of classical trajectories. The calculations use exact 3D classical Hamilton equations in the action–angle variables and nonempirical surfaces of the interaction’s potential energy. The collision parameters are selected by the Monte Carlo method. A statistical analysis of the QC parameters is performed. It is shown that QCs can be both short-lived and long-lived and are characterized by a variety of interparticle separations. Among the total number of collisions, the fraction of QCs increases rapidly with a decrease in temperature. Formulas are given that reveal the contribution of QCs to the cross sections of the rotational RT-relaxation of CH₄. It is shown that in the methane mixtures considered the RT-relaxation in QC-type collisions is much more effective than in ordinary inelastic collisions.