Emission spectroscopic diagnostics of weakly ionized argon-diluted plasmas: glow discharge and inductively coupled plasma

Abstract

Abstract An extensive study of Mn, Fe, Ti, Cr, Cu emission spectra from a Grimm-type glow discharge (GDOES) and an inductively coupled plasma (ICP), in argon, was performed, using the formalism of population functions (experimental Boltzmann plots) and transition rate diagrams. Emission characteristics of both spectral sources were compared, with the following results: in both discharges the excitation of neutral metal atoms (Me I) is dominated by electron impact (EI), however, in the excitation of singly charged ions (Me II) the charge transfer between Ar+ ions and Me I plays a significant role, especially in GDOES. Relative populations of singly charged excited ions compared to the population of excited neutral atoms of the same element are much higher in ICP than GDOES. Deviations from local thermodynamic equilibrium were identified. Besides charge transfer reactions with Ar+ ions they are caused by a low electron density in the plasma. The experimental ‘excitation temperatures’ follow a pattern predicted by computer simulations with a collisional-radiative model: they are lower than the actual electron temperature, while this deviation is greater for the Me I system than Me II.