Vacuum-UV negative photoion spectroscopy of SF5CF3

Ion pair formation, generically described as AB→A++B−, from vacuum-UV photoexcitation of trifluoromethyl sulfur pentafluoride, SF5CF3, has been studied by anion mass spectrometry using synchrotron radiation in the photon energy range of 10–35eV. The anions F−, F2−, and SFx− (x=1–5) are observed. With the exception of SF5−, the anions observed show a linear dependence of signal with pressure, showing that they arise from ion pair formation. SF5− arises from dissociative electron attachment, following photoionization of SF5CF3 as the source of low-energy electrons. Cross sections for anion production are put on to an absolute scale by calibration of the signal strengths with those of F− from both SF6 and CF4. Quantum yields for anion production from SF5CF3, spanning the range of 10−7–10−4, are obtained using vacuum-UV absorption cross sections. Unlike SF6 and CF4, the quantum yield for F− production from SF5CF3 increases above the onset of photoionization.