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

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) x 10(15) particles cm(-3) range under the emission and mass spectrometry. The nitrogen atom concentration [N] is in the (0.1-4)x 1015 particles cm(-3) range under the experimental conditions investigated. For a N-2-0.01%CH4 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, as the pressure decreases from 25 to 12.5 mbar, and the excited ion density [N-2(+)(B)], is 5 x 10(4)-2 x 10(6) particles cm(-3), i.e. 100-1000 times lower than in pure N-2. (C) 1999 Elsevier Science S.A. All rights reserved.