S. Ya. Umanskii

Dynamics of charge transfer Ar++(3P)+He(1S)→Ar+(2P)+He+(2S) at low collision energies: Comparison of experimental results with quasiclassical calculations of the differential cross sections

Differential cross sections of the elementary process Ar++(3P)+He(1S)→Ar+(2P)+He+(2S) at collision energies between 0.6 and 1.6 eV were calculated using the quasiclassical treatment. Analytic potentials providing an approximation of the electronic energy of the system were employed to calculate deflection functions. Coupling of the diabatic terms was evaluated using the asymptotic method, and the Landau–Zener model was applied to account for the transition probability. Semiquantitative agreement of the calculated differential cross sections with those obtained in crossed beam experiments was achieved.

The temperature dependence of the reactions H2(v = 1) + D, H

Abstract The temperature dependence of the rate constant for the reactions H2(v = 1)+D and H2(v = 1)+H was studied using a flow-tube method combined with EPR and thermometric techniques. The rate constants (in cm3/molecule s) were found to be kuD = (2.3 ± 1.3)×10−10exp[−(3200 ± 600)/RT]. knD = (1 ± 0.5)×10−10exp[−(3100 ± 300)/RT]. krD ⩽ 2.7×10−13 over the range 254–367 K for H2(v = 1)+D and knH+krH = (1.8 ± 0.7)×10−13 at 254 K and (3.9 ± 1.0)×10−13 at 298 K for H2(v = 1)+H.

On the mechanism of heterogeneous relaxation of vibrationally excited nitrogen molecules

Abstract The N 2 vibrational deactivation probability ∈ in the case of a collision with a glass surface has been measured over the temperature range 282–603°K for different values of pressure. The observed temperature and pressure dependence of ∈ is interpreted in terms of two different additive mechanisms of the heterogeneous vibrational relaxation. One of these is connected with the physical and the other with the chemical adsorption of the vibrationally excited N 2 molecule.

The I-2(B) predissociation by solving an inverse atoms-in-molecule problem

The valence electronic states of the iodine molecule are analysed by means of a simple atoms-in-molecule model which accounts for the lowest 2P states of iodine atoms and approximates the spin-orbit interaction by its atomic part. For this model, an inverse problem is solved, i.e. non-relativistic potential energy curves and diabatic couplings are determined by a least-squares fit to known relativistic potential energy curves. The resulting adiabatic wave functions are used to calculate the electronic matrix elements responsible for natural, hyperfine and magnetic predissociation of the iodine molecule in the B0+ u: state. The results are in reasonable agreement with experimental data, being stable enough with respect to the variation of input relativistic potentials. They also indicate the importance of diabatic couplings between the non-relativistic states of the same symmetry.

Low-temperature ignition of methane-air mixtures under the action of nonequilibrium plasma

A plasma-chemical kinetic mechanism of the low-temperature (600 < T < 1000 K) oxidation/combustion of methane under conditions of nonequilibrium plasma over a wide pressure range (P = 0.1−100 atm) is developed and verified. The mechanism is comprised of three types of elementary processes: chemical reaction of neutral atoms and molecules, primary plasma-chemical processes involving electrons, and secondary plasma-chemical processes involving atomic and molecular ions and excited species. Application of the developed mechanism to describing the plasma-assisted oxidation of methane shows that this mechanism can describe the experimental results qualitatively and quantitatively.

Dynamics of vibrational energy exchange in collisions of OH and OD radicals with N2. Application to the kinetics of OH-vibrational deactivation in the upper atmosphere

The dynamics of collisions of OH and OD radicals with the N2 molecule is considered. Vibrational energy exchange rate constants are estimated theoretically. The vibration-to-rotation energy exchange mechanism is shown to be the main contribution for these systems. The results are compared with experimental data and the rate constants obtained from the base ground observations of night sky Meinel emission. Rate constants of vibrational-to-vibrational exchange are too low for the collisions of OH with N2 to be important in hydroxil vibrational energy deactivation in the atmosphere.

Energy transfer in collisions of highly vibrationally excited tetrahedral molecules

Abstract Model trajectory calculations of the energy transfer processes in collisions of Ar with highly vibrationally excited CH 4 , CD 4 , SiH 4 and CF 4 are performed. Special attention is payed to the calculation of the energy transferred to active (vibrational) degrees of freedom. The results support the diffusion model of excitation-dissociation and give the low pressure collision efficiency β c which qualitatively agrees with experiment in magnitude and temperature dependence.

On the possibility of improving classic hydrodynamics equations by an increase in the number of hydrodynamic values

Any of the infinite number of invariants of a binary collision of structureless particles was shown to annihilate the collision integral written in the 12-dimensional phase space of two particles. Its own principal hydrodynamic value corresponds to each of these invariants. The six-dimensional phase space of one particle can only accommodate three lower binary collision invariants that allow the integral of collisions to be annihilated. The first equation of the Bogolybov-Born-Green-Kirkwood-Yvon hierarchy is, however, not closed, and the transition from the 6-dimensional phase space to the hydrodynamic stage of description is therefore closed. The Boltzmann hypothesis closes the kinetic equation and therefore opens up the possibility of approximate transition to hydrodynamics. Just the Boltzmann hypothesis allows classic hydrodynamics equations constructed with the use of only three lower principal hydrodynamic values to be substantiated statistically. It should be expected that the neglect of the higher principal hydrodynamic values will limit the applicability range of classic hydrodynamics to states insignificantly removed from the statistical equilibrium state. Most probably, just this limitation is responsible for obvious discrepancy between the results of direct numerical integration of the Navier-Stokes equation and the experimental data on flows that lost stability. The possibility of the improvement of classic hydrodynamics equations is sought on the way toward an increase in the number of principal hydrodynamic values.

Non-Arrhenius behavior of the F+H2 reaction rate at 293–700 K

Abstract Non-Arrhenius behavior was observed in the temperature range 293–700 K for the absolute rate constant for the reaction F + H 2 using an EPR spectrometer combined with a fast-flow system. The measured rate constant (in cm 3 /s) fits the expression k = 2.9 × 10 −13 T exp[−(1390±440)/ RT ].

Roughness simulation for thin films prepared by atomic layer deposition

The kinetic lattice Monte Carlo method for film growth simulation without taking crystallization into account was applied to study the roughness of the HfO2 film grown by atomic layer deposition at 100–500°C from HfCl4 and H2O. The calculations were performed using a simplified kinetic mechanism of the growth of HfO2 films obtained by reducing the detailed kinetic mechanism developed earlier. Ab initio quantum-chemical calculations were performed to determine the kinetic parameters of diffusion processes on the surface of hafnium oxide that could influence film roughness. Because of the special features of atomic layer deposition, the rate of film growth and film roughness were finite even if surface relaxation was ignored. It was found that, irrespective of the temperature, the diffusion of hydrogen and adsorbed HfCl4 complexes did not change the profile of the growing film and only insignificantly increased the mean rate of growth. The results obtained were also qualitatively applicable to zirconium dioxide at fairly low (≤100°C) temperatures in the absence of crystallization.