Electron attachment, ionization and drift in c-C4F8

The pulsed Townsend method has been used to measure the drift velocity v e and the density-normalized effective ionization coefficient (α-η)/ N , (α and η are the ionization and attachment coefficients, respectively) in c-C 4 F 8 over the density-normalized electric field strength E / N , 12 Td⩽ E / N ⩽43 Td and 330 Td⩽ E / N ⩽600 Td (1 Td = 10 -17 V cm 2 ), at pressures between 1 and 7.5 Torr (1 Torr = 133.3 Pa). For 12 Td⩽E/N⩽43 Td, the above parameters were found to be pressure independent, while for the range 330 Td⩽ E / N ⩽600 Td an inverse dependence of the above coefficients was found for gas pressures less than 2 Torr. Such dependence is believed to be due to the autodetachment of the originally formed, unstable parent negative ion c-C 4 F 8 -* . At low E / N , no previous data for v e or (α-η)/ N were found for comparison with the present data. A critical field strength of E / N crit = 439.5 Td, for which α = η, was found to be in good agreement with previous data.