Andrey E. Belikov

Rate constants and rotational relaxation times for N2 in argon: Theory and experiment

Abstract Rate constants and rotational energy relaxation times for N 2 in argon are obtained theoretically and experimentally. Theoretical calculations are performed in the semiclassical centrifugal sudden approximation (SCS) for LJ(12, 6) potential. Experimental rate constants are determined from the rotational level population kinetics in nitrogen free jet, seeded into argon with the help of electron-beam diagnostics. The temperature dependence of the energy relaxation time, calculated from experimental data, is in a good agreement with theoretical prediction.

Temperature dependence of the rotational relaxation time in nitrogen

Abstract An electron-beam fluorescence method has been used to study the temperature dependence of the rotational relaxation time characterizing the R-T energy transfer resulting from the free jet expansion of nitrogen for temperatures in the range 6–320 K. Theoretical values calculated in a semiclassical approximation are in good agreement with the present experimental data. The parameters of the anisotropic part of both the repulsive and attractive parts of the interaction potential have been determined earlier through a fitting procedure using the results of other experiments.

State-to-state rate constants and rotational relaxation time in nitrogen

Abstract A recently developed ‘quasiclassical ECS-E’ fitting law for rotational transition rates has been used for a detailed comparison of theoretical and experimental data on rotational energy relaxation in nitrogen. A wide range of data on line broadening coefficients, ultrasonic absorption, population kinetics of isolated rotational levels exposed to laser pumping and population kinetics in a free jet has been analysed in order to refine the effective intermolecular parameters of the model thus providing a temperature-dependent form of the fitting law from 35 up to 1500 K.

State-to-state rate coefficients for rotational relaxation of CO in Ar

The rotational level populations of CO molecules were measured in CO (<10%)+Ar free jets by electron beam fluorescence (in a stationary jet) and resonantly enhanced multiphoton ionization (in a pulsed jet). The measured evolution of the nonequilibrium rotational energy was used to derive the rotational relaxation cross sections in the temperature range from 7 to 150 K. Using the pressure-broadened linewidth data the state-to-state rotational relaxation rate coefficients were found using the most popular fitting law forms: The modified exponential gap, the statistical polynomial-exponential gap, and the energy corrected sudden approximation. The fitted rates were compared with the experimental and theoretical data presently available in the literature. They were checked also by consideration of the rotational kinetics in free jets and by comparison between the computed and experimental rotational level populations both in near and far regions of a flow.

The rate of collisional quenching of N2O+ (B 2Σ), N+2 (B 2Σ), O+2 (b 4Σ), O+ (3d), O (3p), Ar+ (4p’), Ar (4p,4p’) at the temperature ≤200 K

Rate constants of collisional quenching of the states N2O+ (B 2Σ+u), N+2 (B 2Σ+u), O+2 (b 4Σ−u), O i (3p 5P), O ii (3d 4F), Ar ii (4p’ 2F0) in their parent gases and the states Ar i (4p,4p’[1/2]) in oxygen have been measured by studying Stern–Volmer dependencies in the temperature range from 20 to 200 K. Radiating states were excited by the electron beam. A flow on free jet axis was used as a gas target. Negative dependencies of rate constants on temperature which were obtained are consistent with the available experimental data on rate of internal energy and charge transfer at low energy collisions.

Rotational relaxation time in free jets of He + N2 mixtures

Non-equilibrium rotational energy distributions of N2 in free jets of He + N2 (<5%) were measured by the electron beam technique. The rotational temperature was derived from the spectrum of the first negative system of N2+ induced by high energy (E ∼ 10 keV) electrons. The experimental data were compared with kinetic calculations of rotational energy in free jets based on the linear relaxation equation: dERdt = −(ER−Et)τ. The rotational relaxation times τ were derived from available transport collision integrals, evaluated with three different potential energy surfaces: HFD1, BTT and M3SV. The HFD1 surface leads to an overestimated rate of rotational relaxation. Two other surfaces agree satisfactorily with experiment, similarly as observed by Dickinson et al. for transport coefficients. To decide between BTT and M3SV, more precise measurements should be carried out over a wide temperature range.

Rotational and vibrational excitation of the N2+ (B) state in a He + N2 electron-beam plasma

Emissions of the first negative system of N2+ have been studied in a He + N2(< 5%) mixture activated by a 10-keV electron beam. Flow in the free jet core was used as a gas target. Analysis of both the internal energy distributions in the N2+(B) state and the He density dependecies of the excitation rates have revealed three excitation mechanisms. One of them is the excitation by atomic ions He+ going through the formation of long-living collisional complexes (He.N2)+. This channel produces the vibrational and rotational heated ions N2+(B), with the rotational temperature independent of the rotational distribution in the ground state of the N2 molecule before excitation. This temperature is estimated as T = (900 ± 60) K. The other excitation channels are evidently Franck-Condon processes with the population of vibrational levels according to Franck-Condon factors and with the rotational transition probabilities close to those governed by Honl-London factors in the excitation.

ROTATIONAL RELAXATION OF NITROGEN IN HELIUM

Abstract Rotational level populations of N 2 have been measured in free jets of He + N 2 mixtures by an electron beam technique. The experimental data are compared with kinetic calculations, based on theoretical state-to-state rate constants, obtained by the IOS method with an M3SV potential energy surface. Reasonable agreement of the data substantiates the IOS method down to low (≈ 10 K) temperatures. Other available calculations of rotational relaxation times are compared with the present experimental data.

State-specific reactions HBr+(2Πi,v+)+(H2, HBr)→H2Br+ at low collisional energies

State-specific ion-molecule reactions of H-atom transfer between the HBr and H2 molecules with HBr+(2Πi,v+) were studied in a free jet flow reactor. The selected spin-orbit and vibrational states of the HBr+ ion were prepared by resonance-enhanced multiphoton ionization. All of the reactant and product ions were monitored using a time-of-flight mass spectrometer. Rate coefficients of the HBr+/H2 reaction vary from <2×10−12 cm3/s for the lowest spin-orbit-vibrational state to 2.1×10−11 cm3/s for the highest. Rates for the HBr+/HBr reaction are ∼1.5×10−9 cm3/s independent of the internal state of the ion.

State-specific low temperature reactions of

Abstract State-specific reactions of DBr + ( 2 Π i ,v + ) with D 2 and DBr were studied in a low temperature free jet flow reactor. The selected spin–orbit and vibrational states of the DBr + ion were prepared by resonance-enhanced multiphoton ionization. All of the reactant and product ions were monitored using time-of-flight mass spectrometry. Rate coefficients for the DBr + /DBr reaction are ∼1.4×10 −9 cm 3 s −1 independent of the ion internal state, similar to those for the HBr + /HBr reaction. Rate coefficients of the DBr + /D 2 reaction rise from 0 (lower spin–orbit-vibrational states) to 2×10 −11 cm 3 s −1 (highest energy states) and are observed to follow a mass independent threshold function similar to the HBr + /H 2 reaction.