Rotational temperature measurements in hydrogen discharges

An electrodeless capacitive rf discharge operated at 13.56 MHz, which we used previously in diamond deposition experiments, was placed in a specially constructed furnace in order to control the temperature independently of rf power. Methane highly diluted in hydrogen as well as pure hydrogen were used as process gases. The emitted light from the plasma was investigated by optical emission spectroscopy. The relation between the rotational temperatures determined from the R branch of the G1 Sigma(g)(+) --> B-1 Sigma(u)(+) (0-0) band of molecular hydrogen with furnace temperature, rf power and pressure was investigated. From the results we have to conclude, that the assessed rotational temperature can be used only as a rough value for the gas kinetic temperature.