A flowing-afterglow Langmuir probe apparatus with mass spectral analysis was used to measure rate constants, identify reaction products, and measure branching fractions for electron attachment to 1,2-dichlorohexafluorocyclopentene (c-C 5 F 6 Cl 2 ) and 1,2-dichlorooctafluorocyclohexene (c-C 6 F 8 Cl 2 ) over the temperature range 295–555 K and buffer gas density range of 1.3–2.1 × 10 16 cm −3 . Electron attachment to both of these compounds is efficient over this temperature range and the rate coefficient for attachment is relatively independent of temperature. At 295 K the electron attachment rate coefficient for c-C 5 F 6 Cl 2 is 2.5 ± 0.6 × 10 −7 cm 3 s −1 and for c-C 6 F 8 Cl 2 is 3.5 ± 0.9 × 10 −7 cm 3 s −1 . At 300 K, electron attachment to both neutral reactants is predominantly nondissociative. At higher temperatures, a dissociative reaction channel forming Cl − is observed for both reaction systems. Significant branching fractions for Cl − (≥0.05) are observed at temperatures greater than 425 K for c-C 5 F 6 Cl 2 and at temperatures greater than 375 K for c-C 6 F 8 Cl 2 . Over the temperature range of 300–550 K the branching fractions for formation of the nondissociative and dissociative products were not dependent on buffer gas density in the range of 1.3–2.1 × 10 16 cm −3 .