Measurements by optical and mass spectrometry of the density of active species in the flowing afterglow of a N2/(10−4–10−3)CH4 plasma

Abstract

Abstract The influence of small quantities of methane on the behaviour of the active species N, N 2 (A) and N + 2 (B) has been studied by emission and mass spectrometry. The nitrogen atom concentration [N] is in the (0.1–4)×10 15 particles cm −3 range under the experimental conditions investigated. For a N 2 –0.01%CH 4 mixture, [N] is twice as high as for pure N 2 . The metastable N 2 (A) concentration is approximately 10 11 particles cm −3 , i.e. it varies from 3 to 6 times lower than in pure N 2 as the pressure decreases from 25 to 12.5 mbar, and the excited ion density [N + 2 (B)] is 5×10 4 –2×10 6 particles cm −3 , i.e. 100–1000 times lower than in pure N 2 .