The adsorption of methane by barium films in the presence of a thermionic current

Abstract

The adsorption of methane at pressures of 7×10 -7to 7×10 -6torr has been studied both in the presence and absence of a thermionic current drawn from a tungsten filament, using the capillary flow method of Wagener, and maintaining the pressure over the barium film constant. The pumping speeds of barium films covering up to 160 cm 2 and up to 20 mg in weight under normal conditions were very small and were less than 5 cc/sec at 1.5×10 -6 torr. The presence of an incandescent tungsten filament caused a slight increase in pumping speed of the barium films of about 10–20 cc/sec. Drawing an emission current from the filament appreciably increased the pumping speed of the getter, the increase amounting to 70–100 cc/sec at 1.5×10 -6 torr with a current of 5 mA. The pumping speed was independent of the area and weight of barium film but was approximately proportional to the thermionic current; it was almost independent of the pressure, up to 7×10 -6 torr, and hence the adsorption rate (pumping speed × pressure) was roughly proportional to pressure. The results show that the adsorption rate on barium films of methane activated by electron impact is determined entirely by the frequency of electron-gas molecule collisions. It is not known whether the active species consists entirely of ions or whether non-ionized radicals and molecules resulting from the decomposition of methane are involved.