Rotational Temperature in Helium, Argon, and Oxygen Microwave-Induced Plasmas: Comparison with Translational and Solid Surface Temperatures

Translational temperature ( T g ), rotational temperature of OH ( T r ), and surface temperature ( T s are determined in helium, argon, and oxygen plasmas. Measurements are carried out at different pressures and different flow rates as a function of microwave power input by using various methods (line broadening, pressure rise, spectroscopy, thermocouple, pyrometry). The three temperatures depend on the nature of the gas (oxygen < helium > argon) and increase with power input and pressure. Results show that T g is of the same order of magnitude as T s . But in all experimental conditions, T r is always higher than T g . Therefore, T r is inadequate for estimating T g . When no direct determination of T g is available, T s seems to give a better estimation of this important parameter.