Growth of ionization currents in carbon tetrafluoride and hexafluoroethane

Values of the ionization coefficient α and attachment coefficient η have been obtained in CF4and C2F6at 20°C using the modified Townsend method. In CF4the reduced fieldE/pwas varied from 40 to 90 V cm−1torr−1and the reduced coefficients α/pand η/pwere found to be independent of pressure from 5 to 20 torr. In C2F6the range ofE/pwas from 70 to 190 V cm−1torr−1and the pressure was varied from 2·5 to 30 torr. Values of α/pand η/pare in good agreement at the lower pressures but at 30 torr it was necessary to assume a small detachment coefficient δ/psimilar, equals2 × 10−3cm−1torr−1, in order to obtain consistent results.