Temperature and absolute oh density measurement by the relative emission spectroscopy in diffuse atmospheric-pressure RF glow discharges

摘要

Summary form only given. In recent years, the measurement of absolute densities of reactive species and radicals such as OH is of growing interest for many plasma applications. Many complex techniques, including laser-induced fluorescence (LIF), cavity ring-down spectroscopy, resonant absorption and broadband absorption, have been used to measure absolute OH density. However, the optical emission spectroscopy (OES) has the natural advantage of being non-intrusive, inexpensive, and easy to implement, in comparison with the abovementioned methods.In this contribution, we will extend the use of a selfabsorption model for atomic emission spectroscopy1, 2 to molecular emission spectroscopy, in particular OH(A-X). We propose to analyze the self-absorption effect on rotational lines in the emission spectra of OH(A-X) for the simultaneous measurement of gas temperature and OH(X) density. We apply the model on emission spectra recorded from a 10 cm homogeneous and diffuse glow discharge which is optically thick for the OH(A-X) emission. The effect of gas temperature, rotational temperatures, and spectral resolution of the spectrometer is assessed. The outcomes are compared in detail with OH densities measured by broadband absorption and gas temperatures by OES of N2(C-B) to validate the proposed method. The detection limit of the line integrated OH(X) density with this method is of the order of 2 × 1019 m-2. The accuracy of the density is sensitive to the rotational temperature of the OH(A) state and the nonequilibrium rotational population distribution. The proposed analysis of self-absorbed optical emission spectra is a simple and inexpensive method to determine OH densities, in large volume plasmas although it requires a high-resolution spectrometer.