Laser-induced fluorescence temperature measurements in a dc arcjet used for diamond deposition

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Abstract
Laser-induced fluorescence (LIF) observations of CH and C2 radicals in a dc-arcjet plasma are reported. A hydrogen and methane gas mixture flows through a dc-arc and expands through an orifice in the anode to form a luminous jet; diamond film grows under this jet on a water-cooled substrate. At the substrate position for best diamond growth, laser excitation spectra determine a rotational population distribution of CH(X) and C2(a), which yields Boltzmann gas temperatures of 2100 ± 200 K. The C2 Swan-band emission from the same observation volume yields an excited C2(d) rotational and vibrational population distribution well described by a 5000 K temperature. The difference between the LIF and emission temperatures indicates that chemiluminescent reactions are the dominant excitation mechanism for the optical emission from the gas jet.