Vacuum Ultraviolet Photochemistry of Eco-Friendly Insulating Gas: CF₃SO₂F

Area of Science:

• Physical Chemistry
• Photochemistry
• Mass Spectrometry

Background:

• Trifluoromethanesulfonyl fluoride (CF3SO2F) is an eco-friendly alternative to sulfur hexafluoride (SF6) as an insulating gas.
• Understanding the vacuum ultraviolet (VUV) photochemistry of CF3SO2F is crucial for its application and environmental impact assessment.
• The stability and fragmentation pathways of the parent ion (CF3SO2F+) are key to predicting its behavior under VUV irradiation.

Purpose of the Study:

• To investigate the VUV photochemistry of CF3SO2F in the 11-14 eV energy range.
• To elucidate the dissociation mechanisms and energetics of the CF3SO2F+ parent ion.
• To compare experimental findings with theoretical calculations for a comprehensive understanding.

Main Methods:

• Synchrotron radiation photoionization mass spectrometry was employed to analyze the photoionization products.
• High-level theoretical calculations were performed to determine ionization energies and potential energy surfaces.
• Analysis focused on the appearance energies of fragment ions, particularly CF3+ and SO2+.

Main Results:

• The CF3SO2F+ parent ion is unstable and dissociates into fragment ions like CF3+, SO2+, and SOF+.
• The adiabatic ionization energy (AIE) to the bound A2A″ state was determined to be 12.65 eV.
• Experimental appearance energies for CF3+ and SO2+ align with the AIE of the excited state, not lower predicted values.

Conclusions:

• The CF3+ fragment is formed via a direct predissociation pathway involving a conical intersection.
• The SO2+ fragment arises from a more complex, multistep pathway, explaining its lower intensity.
• These findings clarify the VUV photodissociation mechanisms of CF3SO2F, essential for its use as an SF6 replacement.