Electron-ion recombination rate constants in dense gaseous argon and krypton: Effects of electric field strength and the addition of N2 or CH4

Abstract

The electron mobilities, μe, and electron-ion recombination rate constants, kr, in dense gaseous Ar and Kr with a small amount of N2 or CH4 as a molecular impurity have been measured as a function of electric field strength using a pulse radiolysis dc-conductivity method combined with a new decay-curve analysis method in which a space-charge effect is taken into account to obtain more accurate values of kr. The energy of electrons in recombination is controlled experimentally in two ways; one is heating-up by the electric field and the other is cooling-down by inelastic collisions with additive molecules. A large deviation of kr from the Debye theory obtained in the present experiment has been discussed in terms of the electron mean free paths and electron energies based on recent theories.

Effect of Molecular Additives on Electron Mobility and Electron−Ion Recombination Rate Constant in Dense Gaseous Krypton

“…The assumed density is n = 1.2 × 10 21 cm -3 and temperature T = 291 K. The simulation results are shown in the lower part of Figure , together with the results obtained for pure Kr in our previous study . The upper part of Figure shows the experimental results for the electron mobility in Kr/N 2 mixtures obtained by Takeda et al In both parts of the figure, the results for pure Kr are shown by closed circles, those for c N 2 = 0.5 mol % by open circles, and for c N 2 = 2 mol % by squares. A comparison between the theoretical and experimental results for Kr/N 2 mixtures leads to conclusions very similar to those in the case of Kr/CH 4 .…”

“…The simulation for pure Kr yields k = 0.6 × 10 -7 cm 3 /s, while the corresponding values of k reported by Takeda et al . at the external field of 450, 600, and 750 V/cm are 3.5, 2.1, and 1.3 × 10 -5 cm 3 /s, respectively. The reasons for this disagreement have been thoroughly discussed in ref .…”

“…A comparison of the theoretical results for the recombination rate constant in Kr/CH 4 and Kr/N 2 systems with the experimental data of Takeda et al . is presented in Figures and , respectively.

8 Dependence of the electron−ion recombination rate constant in Kr/CH 4 relative to its value in pure Kr on the concentration of CH 4 .

…”

“…Figure in ref ), which is much closer to our simulation result than the values of Takeda et al . cited above. By extrapolating the results of Hatano 2 to the zero field, we could reduce the discrepancy between the experiment and the theory even further.…”

“…This may significantly increase the recombination rate, even at very low impurity concentrations. Another motivation for this study comes from the fact that the electron-ion recombination rate constants have been recently measured 15 for argon and krypton doped with methane and nitrogen. A direct comparison of the theoretical and experimental data should be helpful in understanding the mechanism of the electron-ion recombination in dense rare gases.…”