Nonlocal nature of the electron energy spectrum in a glow-discharge in pure O-2: II. Actinometry of O(P-3) atoms in a plasma at low gas pressures

Results are presented from measurements of the density of oxygen atoms in t he positive column of a de discharge in pure oxygen by the actinometric tec hnique using Ar atoms. Based on the excitation rate constants calculated us ing two different approaches (namely, the two-term approximation and the Mo nte Carlo method) to solving the Boltzmann equation for a spatially inhomog eneous electron distribution function, the applicability of the actinometri c technique is analyzed. The effects of the discharge kinetics and the nonl ocal character of the electron energy spectrum on the accuracy of actinomet ric measurements are studied. It is shown that the results of measurements depend only slightly on the accuracy with which the electron energy distrib ution function is described. Over a wide range of the reduced electric fiel d E/N approximate to 40-250 Td, the oxygen atom density calculated using th e spatially homogeneous distribution function differs by several percent Fr om that calculated accurately, taking into account the nonlocal character o f the electron energy spectrum. It is shown that using the actinometric tec hnique to measure the absolute concentration of oxygen atoms in a plasma re quires a detailed description of the discharge plasmochemical kinetics, inc luding a thorough analysis of all possible processes (particularly, surface heterogeneous reactions) that determine the density of active particles at low pressures. At the same time, the use of the actinometric technique for monitoring the behavior of the density of oxygen atoms in a plasma is just ified over a wide range of reduced electric fields up to similar to 200 Td when the O(3p(3)P-3p(3)S) transition (lambda = 844.6 nm) is used and the de gree of dissociation is [O]/[O-2] > 0.02. (C) 2000 MAIK "Nauka/Interperiodi ca".