Determination of the Excited State Density Distribution within a Nonequilibrium, Freely Expanding Argon Arcjet Plume

Abstract : The distribution of the population densities of the excited states of argon was determined at two axial positions in the non-equilibrium, freely expanding plume of an argon d-c arcjet. Narrow-line absorption and concomitant radial inversion were used to obtain densities of the first four excited states of argon, which include the two metastable and two resonance states. Abel inversion of the absolute radiance measurements of emission from several spectral lines provided the number density of highly excited states, the excitation or electron temperature, and the electron number density. The distribution functions observed were decidedly nonequilibrium, with the first four excited states ranging from a factor of two to a factor of ten larger than that required for Saha equilibrium with free electron density.