Measurements of electron attachment lineshapes and cross sections at ultra-low electron energies for 2-C4F8, c-C5F8, c-C6F6and C7F8

Electron attachment cross sections are reported in the electron energy range 0-150 meV, and at energy resolutions of 5-8 meV (FWHM), for the molecules 2-C 4 F 8 (perfluoro-2-butene), c-C 5 F 8 (perfluorocyclopentene), c-C 6 F 6 (perfluorobenzene) and C 7 F 8 (perfluorotoluene). Use is made of the Kr photoionisation technique, and measured attachment lineshapes are converted to cross sections by normalisation through absolute attachment rate constants. As in previous results on 2-C 4 F 6 , CFCl 3 , CCl 4 and SF 6 , the present four molecules exhibit resolution-limited onsets at threshold consistent with the s-wave nature of the attachment, and a neutral-negative-ion curve crossing at zero energy.