Temperature variation of positive ion mobilities and conversion rates in neon

Abstract

The temperature variation of electron density decay rates was measured by means of the microwave cavity method following an electrodeless pulsed discharge in neon. The temperature of the gas was varied from 195 to 690°K. For pressures less than about 82 torr (all pressures normalized to 273°K) it was found that ambipolar diffusion was the main loss process during the later part of the afterglow. The interpretation of the measurements over the pressure range was divided into three parts. At higher gas pressures (> 5 torr) the reduced mobility was found to be constant at (645 ± 01) cm2 v-1 sec-1 over the appropriate pressure ranges, and this is attributed to the molecular ions Ne2+. The value of μ0(Ne2+) was found to be independent of gas temperature in the range 195-523°K. At pressures below about 18 torr the `diffusion cooling' phenomenon was observed over the entire temperature range. Extrapolation to zero pressure, at each gas temperature, yielded the mobility values for the atomic ions. Measurements over intermediate pressures (similar 28- similar 4 torr) indicated the presence of atomic and molecular ions. Analysis in this range yielded the mobility of atomic ions as well as the frequency of conversion of atomic into molecular ions by three-body collisions. The values of atomic ion mobility μ0(Ne+) decrease over the whole temperature range, from (430 ± 005) cm2 v-1 sec-1 at 195°K to (309 ± 005) cm2 v-1 sec-1 at 690°K. The conversion frequency of atomic into molecular ions η increases from (115 P02) sec-1 at 195°K to (34 P02) sec-1 at 523°K. When the gas pressure is not corrected to 273°K, the measured values of η follow a Tg-1 temperature dependence law. A value of (0342 ± 0011) A3 was deduced for the polarizability of the neon gas.