Influence of Ar₂⁺ in an argon collisional-radiative model

A nonlinear time-dependent collisional-radiative model for recombining argon is presented. Reactions involving Ar₂⁺ are taken into account and their influence is discussed. It is shown that Ar ₂⁺ may increase the time to reach the quasi-steady-state by a factor of 100. The calculation of the recombination rate coefficient at the quasi-steady-state is presented. An analytical expression is derived and compared with existing literature values. The importance of the increase of the quasi-steady-state time is illustrated by comparisons of excited levels population densities distribution measured in a fast moving plasma where the mechanical time scale is sufficiently short to provide a time-dependent chemistry in a reference frame moving with the flow. The high sensitivity of the results towards the electron number density is pointed out. Finally, the influence of the processes involving Ar₂⁺ on the excitation temperature is discussed.