Growth of ionisation currents in the methyl halides

The prebreakdown ionisation currents between parallel electrodes, d apart, were measured at fixed reduced fields as d was varied. Townsend alpha coefficients have been derived for CH3F, CH3Cl and CH3Br for 26 < E/p < 60 V cm¿1 torr¿1. Appreciable negative-ion formation seemed absent in CH3F and CH3Cl, whereas a small but constant attachment coefficient, ¿/p = 0.015 cm¿1 torr¿1 was observed in CH3Br.