Thermal Electron Attachment to SF6 and CFCl3

Measurements of the attachment rate for thermal electrons to SF6 and CFCI3 have been made using the Cavalieri electron-density sampling technique. The largest single source of error was shown to be uncertainty in the composition of the gas mixtures used in the experiments which contained < 10 ppm of the attaching gases. By paying special attention to this problem, the overall uncertainty in the attachment rates was reduced to less than ± 3 %.