(a) depicts the emission spectra of the glow discharge in 80%
H2+20% Ar and for the gas mixture containing 1.00% CH4. The spectra
present atomic emission lines of Ar and H, and molecular bands of
H2. The identification was done according to [28,29] and spectra are
similar to that presented by [30,31] in ArH2 and H2 discharges, respectively.
The addition of 1.00% CH4 in the glow discharge does not
imply in the appearance of new peaks or molecular bands due to
CH4, at least at sufficient intensity. So in the studied condition, the optical
emission spectroscopy cannot be applied to the process control,
as proposed by [32] for high temperature plasma carburizing.