Vacuum-UV negative photoion spectroscopy of SF5CF3

Ion pair formation, generically described as AB \(\rightarrow\) A\(^+\) + B\(^-\), from vacuum-UV photoexcitation of trifluoromethyl sulfur pentafluoride, SF\(_5\)CF\(_3\), has been studied by anion mass spectrometry using synchrotron radiation in the photon energy range 10-35 eV. The anions F\(^-\), F\(_2\)\(^-\) and SF\(_X\)\(^-\) (x = 1-5) are observed. With the exception of SF\(_5^-\), the anions observed show a linear dependence of signal with pressure, showing that they arise from ion pair formation. SF\(_5^-\) arises from dissociative electron attachment, following photoionization of SF\(_5\)CF\(_3\) 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 SF\(_6\) and CF\(_4\). Quantum yields for anion production from SF\(_5\)CF\(_3\), spanning the range 10\(^{-7}\) to 10\(^{-4}\), are obtained using vacuum-UV absorption cross sections. Unlike SF\(_6\) and CF\(_4\), the quantum yield for F\(^-\) production from SF\(_5\)CF\(_3\) increases above the onset of photoionization.