Microwave measurements of temperature dependence of electron density decay rates in oxygen and oxygen-nitrogen mixtures

A microwave cavity method has been used to measure the electron loss rate in the afterglows of pulsed electrodeless discharges in oxygen and oxygen-nitrogen mixtures. The temperature of the gas was varied from 296 to 870 °K. At higher temperatures the gas pressures had to be increased (up to 114 mmHg at 753 °K) in order to reduce diffusion losses. In pure oxygen and at gas temperatures of 296 and 368 °K a departure from an apparent two-body attachment process was observed as the gas pressure was increased. The measured value of the attachment cross section Q = v a /nv was found to be strongly dependent on gas temperature. It decreased rapidly as the gas temperature was increased from 368 to 753 °K and this is attributed to enhancement of the electron detachment process in this temperature range. Measurements in oxygen-nitrogen mixtures yielded a value of 2.3 × 10 -30 cm 6 sec -1 for the three-body attachment coefficient, in good agreement with the drift tube data, and value of 8.4 × 10 -15 cm 3 sec -1 for the detachment coefficient at a gas temperature of 296 °K.