Ternary recombination of excited Ar+(P1/22) ions, established experimental results reinterpreted with a new extended model.

For many years, the recombination of excited ions of argon, Ar+(P1/22), has been assumed negligible under ambient conditions as compared to the recombination of ground-state ions, Ar+(P3/22). This opinion was confronted with detailed experimental results that seem to clearly support it. Here, we propose a new interpretation in light of our recent calculations, which shows that the recombination efficiency is comparable for both fine-structure states. Noteworthily, in our model leading to a picture consistent with the experiment, residual dimer ions emerge from Ar+(P1/22) due to non-adiabatic dynamics effects and interplay in measured data.

Ab initio transport coefficients of Ar⁺ ions in Ar for cold plasma jet modeling.

Collision cross sections and transport coefficients are calculated for Ar{+} ions, in the ground state {2}P_{3/2} and in the metastable state {2}P_{1/2}, colliding with their parent gas. Differential and integral collision cross sections are obtained using a numerical integration of the nuclear Schrödinger equation for several published interaction potentials. The Cohen-Schneider semi-empirical model is used for the inclusion of the spin-orbit interaction. The corresponding differential collision cross sections are then used in an optimized Monte Carlo code to calculate the ion transport coefficients for each initial ion state over a wide range of reduced electric field. Ion swarm data results are then compared with available experimental data for different proportions of ions in each state. This allows us to identify the most reliable interaction potential which reproduces ion transport coefficients falling within the experimental error bars. Such ion transport data will be used in electrohydrodynamic and chemical kinetic models of the low temperature plasma jet to quantify and to tune the active species production for a better use in biomedical applications.

Ion collision cross sections and transport coefficients extended to intermediate energies and reduced electric fields for He(2)(+) ions colliding with He.

This work is devoted to the calculation of transport coefficients for He(2)(+) ions in gaseous He at intermediate reduced electric fields. These swarm data are of great interest for a better understanding of the mechanisms of formation and propagation of the fast plasma bullets or ionization waves observed in dielectric barrier plasma jet devices. For transport data, the collision cross sections required are determined from several theoretical methods based on quantum, semiclassical, and hybrid approaches and a diatomics-in-molecules model for the potential energy surfaces of He(2)(+). The corresponding collision cross sections are then used in an optimized Monte Carlo code to calculate the ion transport coefficients over a wide range of reduced electric fields extending over the experimental range. Calculated transport coefficients are compared with available experimental data at low electric fields. Moreover, an extrapolation method is used in order to determine the reduced mobility for stronger fields. A critical discussion has been performed on the pertinence and the reliability of these different methods of determination of collision cross sections needed for the calculation of ion transport data. Such ion data will be used in electrohydrodynamic and chemical kinetic models of the low-temperature plasma jet to quantify and to tune the active species production for a better use in biomedical applications.

Measured and calculated SF-6 collision and swarm ion transport data in SF6 -Ar and SF6 -Xe mixtures.

The measurement of the mobility of SF-6 in the mixtures SF6 -Ar and SF6 -Xe is reported over the density-reduced electric field strength E/N 1-180 Td (1 Townsend = 10(-17) V cm(2)), from a time-resolved pulsed Townsend technique. Simultaneously, the mobility of SF-6 in the same binary mixtures has been calculated from a set of collision cross sections for SF-6 -Ar, SF-6 -Xe, and SF-6 - SF6 using a Monte Carlo simulation procedure for ion transport. The good agreement between measured and calculated mobilities in these gas mixtures has led us to conclude that the validation of our cross section sets is confirmed. The elastic collision cross section, a predominant process for ion energies lower than about 10 eV, was determined from a semiclassical JWKB approximation using a rigid core potential model for the ion-neutral systems under consideration. This elastic cross section was then added to several other inelastic collision cross sections found in the literature for ion conversion, electron detachment of SF-6 and charge transfer. Moreover, the calculations of the mobility and the ratios of the transverse and longitudinal diffusion coefficients to the mobility were extended into a much wider E/N range from 1 to 4000 Td. Additionally, we have also calculated the energy distribution functions and the reaction coefficients for ion conversion and electron detachment. Finally, we have shown that the range of validity for the calculation of the mobility in gas mixtures from Blanc's law is only valid for the low E/N region, where the interaction is dominated by elastic collisions and the ion distribution function remains essentially Maxwellian.