Experimental Study of Effect of Rare Gas Admixture on Temperatures of Microwave-Excited Oxygen Discharge Plasma

We examined the effect of a rare gas admixture with oxygen discharge on the vibrational and rotational temperatures of the OH radical by optical emission spectroscopy (OES). We chose helium, neon, argon, krypton and xenon as admixture components with oxygen. We generated a microwave discharge oxygen plasma in a cylindrical quartz tube (26 mm i.d.) with a discharge pressure of about 1.0 Torr. The microwave frequency was 2.45 GHz and the output power was set at 600 W. To obtain the rotational temperature, we measured the band spectrum of the radiative transition A²Σ⁺→X²Π_i of an OH radical. We compared the experimentally measured and calculated spectra to determine the actual vibrational and rotational temperatures of the generated plasma. When the mixture ratio was larger than about 80%, the vibrational and rotational temperatures markedly changed, with depended on the mixed rare gas species. The difference in temperature change is discussed from several physical viewpoints.