Electron impact ionization studies for SF5CF3

Electron impact ionization cross sections measured close to threshold are reported for the newly discovered greenhouse gas SF5CF3. No stable parent ion is detected but several cations are detected and their appearance energies (AE) have been measured. The AE (CF3+/SF5CF3) = 12.87+/-0.10 eV is in excellent agreement with a recently reported value derived from a photoelectron-photoion coincidence experiment. Other ion thresholds are: AE (CF+/SF5CF3) = 24.44+/-0.10 eV, AE (CF2+/SF5CF3) = 17.80+/-0.50 eV; AE (SF+/SF5CF3) = 12.66+/-0.20 eV; AE (SF3+/SF5CF3) = 14.48+/-0.10 eV; AE (SF5+/SF5CF3) = 13.16+/-0.60 eV. Two thresholds are suggested for AE (SF4+/SF5CF3) = 16.10+/-0.30 and 12.10+/-0.30 eV. A tentative assignment of an AE for SF2+/SF5CF3 of 15.6+/-1.0 is also given. These results confirm that SF5CF3 is unlikely to be photolysed in the lower stratosphere and therefore will have a long lifetime against solar photodissociation.