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Recombination of singly charged heavy Cs+ and Br– ions with stabilization with neutral Ar or Xe atoms was studied by the classic trajectory method in the range of ion collision energy and third body energy from 1 to 10 eV. The elementary reaction of recombination was studied on the potential energy surface (PES), which quantitatively reproduces the experimental results of collision-induced dissociation of CsBr molecules (the reverse of recombination). An analysis of the statistically reliable number of trajectories revealed a complex multifactor dynamics of recombination, which involves various mechanisms whose realization depends both on the mass and energy ratio of colliding particles and on the PES structure and spatial configurations of collision determined by impact parameters, orientation angles, etc. The molecules that formed as a result of recombination have nonequilibrium vibrational energy distributions and rotational energy distributions comparable to equilibrium.

Using the method of classical trajectories, the motion of a pair of ions Cs+ and Cl– in three non-convex closed cavities of complicated geometry containing neutral cylindrical “crosspieces” and charged spherical “nuclei” is simulated. The collisions of the ions with the cavity boundary, crosspieces, and nuclei are supposed to be inelastic. The signs of the charges of the nuclei are varied. In each cavity, in one of the calculation series, the nuclei are assumed to be shielded (to carry charges smaller than 1 a.u. in absolute value), whereas in another calculation series, the possibility of the mutual neutralization of an ion and an oppositely charged nucleus at their encounter is taken into account. The statistics of various events, such as the “stickings” of ions to nuclei, neutralizations of ions and nuclei, collisions of ions with obstacles, recombinations of ions, and dissociations of the CsCl ionic-bond molecule are analyzed.

We describe a hard sphere model of direct three-body recombination of the Cs+ and Br− ions in the presence of neutral atoms Hg, Xe, Kr, or Ar as the third bodies. Calculations are carried out for the ion approach energy and the third body energy in the range from 1 to 10 eV under the assumption of non-central approach of the ions. The calculation results include the dependences of the total recombination probability on these energies as well as the opacity functions for two impact parameters and the dependences of the recombination probability on the angles determining the mutual orientation of the velocities of the reagents. The classification of the three-body collisions according to the sequences of pairwise encounters of the particles is considered. The most widespread mechanism of energy removal from the ionic pair is a single impact of the third body with the Br− ion.

The dynamics of the three-body recombination of the Cs+ and Br− ions with the formation of products with the lowest internal energy in the presence of the neutral atoms R = Hg, Xe, and Kr as third bodies is studied. The efficiency of the process is characterized by the effectivity function, which represents the dependence of the internal energy of the nascent molecule on the ion encounter energy and the third body energy. The Hg and Xe atoms are demonstrated to exhibit similar efficiencies in stabilizing the CsBr molecules, significantly superior to that of the Kr atom. The effectivity of each third body as an acceptor of excess energy of the molecules formed in recombination is determined by the structure of the potential energy surface of the individual R-Cs+-Br− system, the masses of the third bodies, and the dynamics of three-body collisions leading to recombination.

Using the method of classical trajectories, we have simulated the motion of a pair of ions Cs+ and Cl− in ellipsoidal cavities containing neutral cylindrical “crosspieces” and charged spherical “nuclei” (both the signs and the absolute values of the charges of the nuclei were varied). Both elastic and inelastic encounters of the ions with the cavity boundary, crosspieces, and nuclei are considered. Most attention is paid to the statistics of the “captures” of trajectories by the nuclei (for elastic encounters of the ions with the obstacles) and to that of the “stickings” of the ions to the nuclei (for inelastic encounters), as well as to the statistics of the ion recombination events and the dissociation events of the corresponding molecule with an ionic bond. The dynamical consequences of nuclei shielding (i.e., a decrease in the absolute values of the nuclei charges) have been determined.

We have studied the kinematic conditions for the formation of the most stable products of direct three-body recombination of ions Cs+ and Br− in the presence of a third-body Xe atom. As the energy of the ions’ central encounters and the energy of the third body range from 1 to 10 eV, the minimal residual energy of the recombination products is found to lie in the interval 0–0.7 eV. The formation of the recombination products with the minimal internal energies is yielded by collisions of the three particles in a triangular configuration in an impact parameter range from 0 to 2.7 a.u. The mutual orientation angles of the vector of the relative ion velocity and the vector of the third body velocity affect the formation of products with the minimal internal energy rather slightly. In most cases, stabilization of the CsBr molecules and high efficiency of the energy transfer to the third body are observed in configurations of the closest approach of the particles with interionic distances close to the equilibrium distance in the CsBr molecule.

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.

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.

Using the method of classical trajectories, we have simulated the motion of a pair of oppositely charged ions in spherical and ellipsoidal cavities, including cavities that contain cylindrical “crosspieces” and positively charged “nuclei.” We supposed that each of the ions reflected off the cavity wall, crosspieces, and nuclei according to the elastic impact law. Most of attention is focused on the statistics of the events of ion recombination and those of dissociation of the corresponding molecule with an ionic bond. When nuclei are absent, recombination and dissociation events are possible only on collisions of the ions with the cavity wall or crosspieces. In the presence of nuclei, on the other hand, the major part of the events occur in time intervals between the collisions of the ions with the cavity wall, crosspieces, or nuclei.

The influence of interaction potential parameters of likely charged ions on cross sections of various channels of a reaction of a pair of diatomic molecules with ionic bonds was studied in terms of quasi-classical trajectory simulation with the use of linear mean-square regressions. In the regression approach, the dependence of the cross section of a given reaction channel on potential parameters at each fixed collision energy is approximated by a linear function. We determined the region of softness parameters of the Cs+-Rb+ and Cl−-I− interaction potentials. This region was optimum for the reproduction of experimental excitation functions of atomic and complex positive ions for the CsCl + RbI → products reaction.

By means of quantum mechanical simulation of the reaction F + H2(v = 0; j = 0, 1, 2) → H + HF(v′, j′) on the Stark-Werner ground state potential energy surface at collision energies of 1.84, 2.74, and 3.42 kcal/mol, we have analyzed interference of the “partial waves” corresponding to different values of the total angular momentum J. As the vibrational quantum number v′ of the HF(v′, j′) product increases, the interference for the HF forward scattering becomes noticeably more constructive. This is probably the reason for the maximum in the angular distributions of the HF(v′= 3) molecules at small scattering angles that was discovered experimentally by D.M. Neumark, A.M. Wodtke, G.N. Robinson, C.C. Hayden, and Y.T. Lee, J. Chem. Phys. 82 (7), 3045 (1985) at the same collision energies. We have also determined the intervals of J values most effective for forward scattering of the HF(v′, j′) molecules.

The design of a microwave source in which a discharge is initiated by an electromagnetic surface wave at 2.45 GHz is described. A stable discharge was supported at a gas pressure p0 exceeding the atmospheric pressure in He, N2, and in H2-Ar, H2-He, and O2-He mixtures in a 2-mm inner diameter quartz tube with a 0.15-mm diameter nozzle at a 50- to 115-W microwave power. A degree of dissociation of up to 80% was reached for pure H2 at p0 = 6 Torr and a 6% mixture of H2 and He at p0 = 50 Torr. When p0 increases to 19 Torr for H2 and to 300 Torr for the mixture, the hydrogen-atom beam intensity, in spite of a decrease in the degree of dissociation, increases due to narrowing of the beam particle velocity distribution.

The absolute values of the efficiency of detection of Cs+ and Cl- ions with energies of 1600 eV have been measured with a ВЭУ-7-2 microchannel electron multiplier. The relative detection efficiencies as functions of the potential of the input surface of the microchannel plate have been assessed. It has been revealed that the absolute values of the efficiency of detection of Cl- and Cs+ ions differ significantly and amount to 36 and 6%, respectively, at input ion currents of ≤2 × 10−14 A.

We studied the nature and collision energy dependence of the maximum that appears in the angular distributions of the HF (v′ = 3) product of the F + H2 (v = 0; j = 0, 1, 2) → H + HF (v′, j′) reaction at small scattering angles θ in the center-of-mass frame. This maximum and its increase as the collision energy increased were discovered in the well-known experiment described by D.M. Neumark, A.M. Wodtke, G.N. Robinson, C.C. Hayden, and Y.T. Lee, J. Chem. Phys. 82 (7), 3045 (1985). In order to determine the nature of the maximum, we performed quantum-mechanical simulation of the reaction on the Stark-Werner ground state potential energy surface at collision energies of 1.84, 2.74, and 3.42 kcal/mol corresponding to the above-mentioned experiment and calculated the vibrationally and rotationally resolved differential cross sections dσv′j′/dΩ of the reaction. The maximum under consideration was found to be due to a superposition of two effects, namely, the absence of HF (v′ = 3; j′) products with large j′ because of energy restrictions and an increase in the relative amplitude of quantum-mechanical oscillations on dσv′j′/dΩ cross sections at small j′ and θ as v′ increased. Oscillations on dσ3j′/dΩ cross sections with small j′ are responsible for the maximum observed.

A simple and sensitive method is proposed for studying gas-dynamic seeded beams containing molecules of some salts of alkali metals and thallium with ionic bonds. This method is based on the use of dissociation of these molecules induced by collisions with xenon. A secondary electron multiplier serves as the detector of a molecular beam. The proposed method has been tested on a seeded gas-dynamic beam of CsCl molecules at a pressure of the carrier gas (hydrogen) of 1–5 atm and with energies no higher than 20 eV. This method has shown high accuracy and reproducibility of results.

A high-efficiency ion source for a mass-spectrometer’s detector of molecular beams and their scattering products is described. The ion source is designed according to a scheme of impact ionization of a beam particle by a longitudinal electron beam in a magnetic field with a strength of up to 130 mT. The design of the source developed is very flexible and has no limitations for use in any experiments with molecular beams. An ionization efficiency of particles of an atomic helium beam of 10−3 ions/atom has been achieved. The useful signal-to-background ratio in the detector’s chamber is 3 × 104 during detection of ions with mass-to-charge ratio m/q = 4 amu.

The F+D 2 elastic scattering as well as the D 2 ( j i =0 → j f =2), D 2 ( j i =1 → j f =3) and, for the first time, D 2 ( j i =0 → j f =4) inelastic rotational transitions have been measured in a crossed molecular beam experiment at a center-of-mass collision energy of 112±2 meV. Differential cross-sections for the measured rotational transitions have been calculated on three different potential energy surfaces (Takayanagi–Sato, DMBE-6SEC of Truhlar and coworkers, and Stark–Werner) using different quasiclassical and semiclassical techniques. Although an overall qualitative agreement is found between the experimental and computed differential cross-sections, significant discrepancies are also apparent. In particular, the dynamical calculations lead to a systematic underestimation of the scattering yield into the non-reactive scattering channels, which can be attributed to shortcomings in the topography of all the three surfaces probed. Replacing the free deuterium molecule with a rigid or a vibrating rotor (both of these models exclude reaction) in the dynamical treatment considerably reduces the disagreement between the experimental and the calculated differential cross-sections for the different inelastic transitions.

We compute the rotationally resolved differential cross sections for F(2P3/2)+D2(v=0,j) inelastic scattering as well as opacity functions for D2 rotational excitation and the reaction F+D2→D+DF. Two values of the collision energy (89.7 and 187 meV) and two initial D2 rotational states (j=0 and j=1) are probed. Four calculation techniques have been compared: the quasiclassical trajectory approach and the Wigner method on the ground state (12A′) surface, wave packet propagation (with the D2 vibrational degree of freedom treated quantum mechanically) on the 12A′ surface, and wave packet propagation on the two coupled surfaces 12A′ and 22A′. The effect of the nonadiabatic spin–orbit coupling on the nonreactive F+D2 scattering is almost negligible, whereas the reaction cross sections in the two‐surface wave packet propagation treatment are considerably smaller than those in the calculations taking into account the ground state surface only.

We compute the vibrationally resolved integral cross sections σ R (ν′), differential cross sections, and opacity functions for the reaction F + H 2 ( ν = 0, j = 0, 1) → H + HF( ν ′, j ′) on the 6SEC potential energy surface by the quasiclassical trajectory technique as well as the Wigner method. In both cases, the Langer correction of the initial H 2 rotational energy is implemented. The results are compared with the recent quasiclassical trajectory calculations on the same surface without the Langer correction and quantum mechanical calculations. It is shown that use of the Wigner phase space functions to describe the H 2 and HF vibrational degrees of freedom reduces the total integral cross sections, smooths the selective HF( ν ′ = 3) forward peak in the HF center-of-mass angular distributions, and dramatically increases the σ R ( ν ′ = 3)/ σ R ( ν ′ = 2) vibrational branching ratio. These results indicate that the disagreements between the quasiclassical trajectory cross sections and the quantum mechanical ones observed in the previous works cannot be minimized by just a proper choice and weighting of the initial conditions in the quasiclassical trajectory calculations.

The molecular complex formation (CF) reaction Hg+CsBr→HgCs + +Br − , competitive to the collision-induced dissociation (CID) Hg+CsBr→Hg+Cs + +Br − was studied in crossed molecular beams. The rotatable mass-spectrometer detector made it possible to measure the branching ratio CID/CF in the translation energy range between 5.2–7.9 eV, as well as the angular and energy distributions of positive ions. The branching ratio is an order of magnitude greater than for the Xe+CsBr reaction. HgCs + ions were found only to backscatter. A 2D impulsive model shows two distinct reactive geometric configurations, which both lead to backscattering. The key role of the internal molecular motion is also predicted by the impulsive model.

The 3D trajectory simulation of the CID reaction Hg + CsBr → Hg + Cs + + Br − has been carried out. The potential energy surface was constructed using the pair HgKr and HgXe potentials. The laboratory-flux contour plots of all the products have been calculated. The Cs + distributions agree with those measured earlier in crossed molecular beams. The distribution of each product consists of two distinct scattering zones which are found to be connected with two collision orientations: Hg striking the Br end and the Cs end of the molecule. The most preferable collision configuration is the “perpendicular Br-head-on” encounter. The “on-Cs” encounters become relatively more important as the collision energy increases. The portion of near-collinear encounters is independent of the energy.

The total and double differential cross sections of the reaction Hg+CsBr→Hg+Cs + +Br − were measured using a molecular-beam technique. The excitation function is similar to that obtained earlier for the collision-induced dissociation of alkali halides by inert gases. The angular distribution of Cs + becomes broader as the collision energy increases. The energy distribution of Cs + at small scattering angles has two distinct peaks which are drawn together as the angle increases. This leads to the horseshoe-like shape of the contour plots (velocity-angle) of the intensity of Cs + scattered. The structure of the double differential cross section is connected with the orientation effects.

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.

Double-differential cross sections are very sensitive to details of the molecular interaction. This study of the applicability of the momentum model for dissociative ionization involves comparing such cross sections as calculated exactly by the classical-path method and within the framework of the model. There is good agreement between the model and exact results, which indicates that even at energies close to threshold, where the conditions for the momentum model are generally violated, the model still gives good results. A substantial advantage of the model is that it requires computer run time less by three orders of magnitude than exact path methods. The latter is particularly important in calculating the angular and velocity distributions of the reaction products, when it is necessary to analyze a very large number of paths leading to reaction. The total cross section for these processes is small (about 1 A2), so the necessary number of classical paths may be 105.

Using the quantum mechanical path integral Monte Carlo method, we simulated parahydrogen clusters (j = 0) and clusters doped with several (up to 6) orthohydrogen molecules (j = 1), with the total number of molecules ranging from 4 to 40 at temperatures of 1.5, 3, and 4.5 K. Some energy parameters (including the chemical potentials) and spatial characteristics of the clusters are found. At a temperature of 1.5 K, as the total number N of molecules in the cluster increases, the chemical potential and the rotational energy of the clusters attain local minima at the same geometrically determined values of N (the magic numbers). The ortho-molecules exhibit a larger probability (compared to the para-molecules) to reside in the central region of the cluster and a smaller probability to be located near its surface. This effect is enhanced as the number of orthohydrogen molecules in the cluster increases, the total number N of molecules grows, or the temperature is lowered.