FIG. 4.
Optical emission spectra of the He/H2/CH4/N2 microwave plasmas with different ratios of N2/CH4: (a) N2/CH4 = 0.4 and (b) N2/CH4 = 0.05. It is to be noted that the intensity scales in the two spectra are different; CN peaks increase in intensity by a factor of ten in (a).