Detection of Nitrogen Metastable Molecules by using the Threshold Ionization Mass Spectrometry.

Abstract

N2(A3∑u+) state has a longer radiation life time and its electron energy is high. Accordingly, it is expected to accelerate chemical reactions in the space where many metastable molecules accumulate. Thus, it is important to detect metastable molecules and to evaluate its number density. The authors used the threshold ionization mass spectrometry to detect N2(A3∑u+) state in nitrogen plasma. A quadrupole mass spectrometer (QMS) was used and its electron energy for ionization was controlled from 8 eV to 25eV. Magnitude of the QMS signal was compared with the ionization cross section of N2(A3∑u+)state by electron collision and its number density was estimated. The dependence of N2(A3∑u+) density on discharge current and the spatial distribution of its density were measured using the method. From the results, it was confirmed that the density of N2(A3∑u+) increased proportionally to discharge current and its density decreased rapidly in the vicinity of glass wall faced to discharge space.