Measurements of the gas kinetic temperature in aCH4-H2discharge during the growth of diamond

Experiments to study the gas kinetic temperature in a dc hollow cathode discharge have been carried out under conditions suitable for diamond growth using ${\mathrm{CH}}_4$-${\mathrm{H}}_2$ mixtures as the feed gas. The gas kinetic temperature is shown to be equal to the rotational temperature for particular emission bands in ${\mathrm{H}}_2$ and in CN in a ${\mathrm{CH}}_4$-${\mathrm{H}}_2$ discharge containing a small ${\mathrm{N}}_2$ impurity for total pressures above 10 Torr. The gas temperature can be obtained by measuring relative line intensities in emission of either the R branch of the ${\mathit{G}}^1$ ${\mathrm{\Sigma }}_{\mathit{g}}^{+}$→B ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$(0-0) band of ${\mathrm{H}}_2$ or the R branch of the ${\mathit{B}}^2$ ${\mathrm{\Sigma }}^{+}$→X ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0-0) band of CN. The (0-0) symbol represents a band of transitions occurring between the levels with 0 vibrational quantum number in the upper electronic state and the levels with 0 vibrational quantum number in the lower electronic state. These measurements of gas kinetic temperature in a ${\mathrm{CH}}_4$-${\mathrm{H}}_2$ discharge using optical emission spectroscopy have been confirmed by two different experiments using laser-induced fluorescence.