The vacuum ultraviolet (VUV) photochemistry of trifluoromethanesulfonyl fluoride (CF3SO2F), a promising eco-friendly insulating gas to replace sulfur hexafluoride (SF6), was investigated in the 11-14 eV energy range by using synchrotron radiation photoionization mass spectrometry and high-level theoretical calculations. It was found that the CF3SO2F+ parent ion formed from VUV photoionization is not stable and dissociates into CF3+, SO2+, and SOF+ fragment ions. The vertical ionization energy (VIE) of the parent molecule to the repulsive X2A' cationic state was calculated to be 13.46 eV, while the adiabatic ionization energy (AIE) to the bound A2A″ state was determined to be 12.65 eV. Notably, the experimental appearance energies of the CF3+ and SO2+ fragments coincide with the AIE of the first excited state (A2A″), rather than the lower appearance energies predicted from ground-state potential energy surfaces. In addition, the dissociation mechanisms to produce CF3+ and SO2+ fragment ions were discussed in detail. For CF3+, photoexcitation populates the bound A2A″ state, which then crosses via a conical intersection to the repulsive X2A' state, leading to direct dissociation into CF3+ + FSO2. This predissociation pathway governs the experimental onset of the m/z = 69 signal. The m/z = 64 signal, corresponding to the SO2+ fragment, is less intense than the m/z = 69 signal because its formation involves a more complex, multistep pathway. This pathway needs isomerization and crossing another conical intersection, making it less favorable than the direct fragmentation that produces the CF3+ fragment.
Zou et al. (Fri,) studied this question.