A collisional radiative model was developed in order to investigate the influence of dissociative recombination on the Saha–Boltzmann plasma equilibrium. As the dissociative recombination products are not well known, their relative importance was tested through comparison with the distribution of line intensities obtained in a microwave argon discharge produced at atmospheric pressure by a surface wave. It was found that the main dissociation products are the ground state and the 4s levels, the 5p and upper levels playing a negligible role. Because the higher levels are only weakly affected by dissociative recombination, they remain in partial local thermodynamic equilibrium. Therefore, the excitation temperature determined from these levels adequately describes the electron temperature. The model well reproduces experimental measurements of excitation temperature, rotational temperature, electron density, and absolute populations of the excited levels.

In this work we propose a criterion to apply the Abel inversion in the case of a small set of experimental data to be used in laboratory plasmas. The Nestor-Olsen method, spline interpolation, and Fourier transform Abel inversion have been compared in order to study the influence of statistical noise and the number of sampled data. The application of this criterion permits us to obtain a radial distribution of the plasma parameters (densities and temperatures) from the spectral line profiles emitted by the discharge. The proposed criterion has been tested using the lateral intensities of several lines emitted by a microwave helium plasma column generated at atmospheric pressure.

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