Dynamics of two-stage direct three-body recombination of ions

Highlights: ► Direct recombination of Cs cation and Br anion in the presence of Xe is studied. ► Quasiclassical trajectory method is employed on a reliable PES. ► The ion closest approach and energy removal by Xe are separated by a varied time lag. ► In this general new two-stage model we propose, any stage can occur first. ► A one-stage process with zero lag and a delay of Xe exhibit quite different dynamics. - Abstract: Single-stage three-body recombination of ions and recombination via intermediate complex formation can be considered as two limiting cases of a general mechanism involving two stages separated by some time interval T, namely, energy removal by the third body and closest approach of the ions. Any of these can occur first. Particular dynamics of nascent molecule stabilization is determined by various kinematic parameters including two collision energies and the lag T. In this paper, recombination dynamics of the Cs+ and Br− ions in the presence of the Xe atom is studied by quasiclassical trajectories. If T vanishes (one-stage process), stabilization proceeds chiefly via energy transfer in encounters of Xe with both ions approaching each other. If the energy removal stage is late, dynamics changes drastically, stabilization occurring via interaction of Xe mainly with only one ion. This three-body recombination mechanism may be of considerable importance at low pressures in gas medium