Diagnostics of heterogeneous processes with the participation of radicals by time-resolved actinometry

Abstract

A method is proposed for measuring the probabilities of the heterogeneous loss of radicals in a gasdischarge plasma. The method is based on the time-resolved modulation actinometry. It is shown that this method is applicable for O, H, F, and CF² radicals. The probabilities of the loss of these radicals on the discharge tube wall are measured in a dc glow discharge. It is shown that the measurement results do not depend on which radical’s emission line is used. The measurement results are only slightly affected by the dissociative excitation of the radical’s emitting states and the background emission from the plasma. It is shown that the technique proposed is similar to the method of laser-induced fluorescence and provides a fairly high accuracy when measuring the probabilities (up to γ _R∼10⁻²–10⁻¹) of the surface loss of radicals in a gas-discharge plasma. In contrast to the LIF method, this technique allows one to acquire a large amount of experimental data over a reasonable time interval (up to one thousand of γ _R measurements per hour). This feature is an important and necessary condition for a thorough study of the surface reactions and the complicated many-parametrical mechanism for the heterogeneous loss of radicals.