V. M. Akimov

Ionic dissociation of CsBr induced by collisions with Hg: molecular-ion formation

Abstract 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 optimization of potential energy surface parameters for the CsCl + RbI system with the use of linear regression analysis

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.

Excitation functions of cation formation in collisions of diatomic molecules with an ionic bond: CsCl + RbI

The excitation functions for the formation of cations Cs+, Rb+, CsRbCl+ and CsRbI+ in collisions of alkali-metal halide molecules CsCl and RbI have been measured in crossed molecular beams for the collision energy ranging from 3 to 10 eV. Trajectory simulation of dissociative processes in the CsCl + RbI system has been performed on a potential-energy surface chosen to be the sum of six pairwise interaction potentials. The calculated excitation functions agree well with the experimental data. Simulation of the CsCl + RbI reaction by a hard-sphere model has also been carried out.

On the maximum in the differential cross sections of the F + H2 reaction in the region of small scattering angles

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.

Structure of small hydrogen nanoclusters containing ortho-molecules

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.

A microwave discharge source operating at pressures of several atmospheres

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.

Efficiency of detection of Cs+ and Cl− ions with a ВЭУ-7-2 microchannel electron multiplier

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.

A simple method for measuring time-of-flight spectra of a gas-dynamic molecular beam

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.