A simplified approach to describing the kinetic properties of impurity ions in a weakly ionized helium plasma

Using an approximate approach that is valid for a large ratio of the ion mass to the mass of the neutral particle, the mobility of ${\mathrm{O}}_2^{+}$, ${\mathrm{N}}_2^{+}$, ${\mathrm{O}}_2^{-}$, and ${\mathrm{O}}_4^{-}$ ions was calculated in helium and good agreement was obtained with the available results of Monte Carlo calculations and experimental data at high values of the reduced electric field. This simplified approach was used to determine the average energy of ${\mathrm{O}}_4^{-}$ ions and the rate constants of dissociation of these ions in helium. The obtained ion characteristics were compared with the results of more accurate calculations using the Monte Carlo method. Good agreement has been obtained between these two approaches for the average ion energy, but for the dissociation rate constant the difference is quite significant, reaching an order of magnitude or more. It was shown that this difference is associated with the peculiarities of the energy distribution of ions for a large ratio of the ion mass to the mass of the neutral particle.