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Abstract We propose a hard sphere model of bimolecular recombination RM+ + X– → MX + R, where M+ is an alkali ion, X– is a halide ion, and R is a neutral rare gas or mercury atom. Calculations are carried out for M+ = Cs+, X– = Br–, R = Ar, Kr, Xe, Hg, for collision energies in the range from 1 to 10 eV, and for distributions of the RM+ complex internal energy corresponding to temperatures of 500, 1000, and 2000 K. The excitation functions and opacity functions of bimolecular recombination in the hard sphere approximation are found, and the classification of the collisions according to the sequences of pairwise encounters of the particles is considered. In more than half of all the cases, recombination occurs due to a single impact of the Br– ion with the R atom. For the recombination XeCs+ + Br–, the hard sphere model enables one to reproduce the most important characteristics of the collision energy dependence of the recombination probability obtained within the framework of quasiclassical trajectory calculations.

The direct three-body recombination reactions Cs+ + X− + R → CsX + R (X = F, I and R = Ar, Xe) are studied within the quasiclassical trajectory method using diabatic semiempirical potential energy surfaces, the encounters of the ions being non-central. The collision energies range between 1 and 10 eV (values typical for low temperature plasma), while the so-called delay parameter, which characterizes the delay in the arrival of the neutral atom R in relation to the time instant when the distance between the ions attains its minimum, is equal to 0 or 20%. The calculation results include the recombination excitation functions, the opacity functions, and the vibrational and rotational energy distributions of the recombination products. All the four reactions considered exhibit similar overall statistical dynamics, but each process has its own features. On the whole, for both the recombining pairs Cs+ + F− and Cs+ + I−, xenon is more effective than argon as an acceptor of excess energy from the ion pair. The rotational energy distributions of the salt molecules CsF and CsI are almost equilibrium, whereas the vibrational energy distributions are strongly non-equilibrium.

The design of a source of a seeded supersonic beam of alkali halide molecules or other vaporized solids is described. At a carrier gas (hydrogen or helium) stagnation pressure of 0.5–5 atm, a stagnation temperature of 1000 K, and a partial seed species pressure of 10–2 Torr, the intensity of the salt beam was 1014 sr–1 s–1 and the energy of molecules in the beam varied from 5.5 to 7.5 eV for a mixture with helium and from 7.5 to 15.5 eV for a mixture with hydrogen. The modular design of the source provides the easy replacement of its functional units.

We compare the dynamics of two elementary reactions of recombination of atomic ions, namely, of the termolecular process of two ions and the third body (1) and of the bimolecular interaction of an ion with the diatomic cluster (2) consisting of the second ion and the neutral atom. It is shown that, despite the fact that both processes yield the same products, the main dynamical characteristics of these processes differ. First of all this concerns the excitation function which confines recombination for (2) by a collision energy up to 2 eV. The opacity functions of both processes have different structures. The distributions of the product vibrational energy in both the processes exhibit a non-equilibrium character, while the rotational energy distributions are equilibrium.

The detailed dynamics of direct three-body recombination of the Cs+ and Br− heavy ions in the presence of the Xe atom as a third body is studied by the quasiclassical trajectory method. A potential energy surface that quantitatively correctly describes the dynamics of the reverse process of ion formation induced by collisions of CsBr with Xe is used. Depending on the impact parameter of the third body, the stabilization of the product molecule proceeds by several different mechanisms. At impact parameters of bR ≤ 7 au, the stabilization of the nascent molecule is largely controlled the repulsion potential between one of the ions or both the ions and the third body. The energy transferred to the third body does not depend directly on the repulsive potential energy between the ion and the third body. The phase of collision of the ions at the instant of closest approach plays a key role in the process of energy transfer. For collinear collision configurations of the three particles, the ion-Xe shallow potential wells are demonstrated to produce a noticeable effect.

The potential energy surface describing quantitatively the dynamics of the collision induced dissociation reactions CsBr + Xe → Cs + + Br − + Xe, CsXe + + Br − is used to explore detailed dynamics of the reverse process of direct three-body recombination of the Cs + and Br − ions undergoing a central collision. For a stepwise analysis of the course of the elementary process, visualization of the trajectory and of the energy state of each pair of the particles is employed. Several different mechanisms of the reaction are found. Their occurrence depends on the impact parameter of the collision of the third body with the recombining pair and on the angles determining the spatial orientation of the ion velocities. The major role in stabilization of the recombination products is played by the repulsion potentials between the ions and the third body, but the amount of energy transferred depends not only on the repulsion interaction strength. Recombination is shown to be able to happen for very low energies of repulsion between the third body and the ions and even in the complete absence of repulsion. In all the cases, the particular recombination mechanism is determined by the dynamical features of the collision. The relation between the kinematic parameters of a collision of the three particles and the recombination mechanism is considered.

A method for studying the detailed dynamics of an elementary process by the visualization of the trajectory of collision of initial particles was suggested. The method has serious advantages compared with graphic processing of the calculated data and provides a high degree of visualization of the calculation results and the possibility of direct comparison between changes in interaction configuration and the energy characteristics of each pair of interacting particles and the total potential energy of a system. The method was used to analyze the detailed dynamics of the collision-induced elementary process of CsBr dissociation. The possibility of elementary process branching because of a change in the sign of the radial component of the generalized momentum of a pair of atoms in a molecule was analyzed.

Trajectory model for collision‐induced dissociation of two molecules with ionic bond is developed on the base of potential energy surface, which ensure quantitative agreement of calculated data with experimental results. Dynamics of interaction is discussed on the bases of the most typical trajectories and angular distributions of the products of interaction.