Mechanism for Electron-Induced SF5CF3 Formation in Condensed Molecular Films

Abstract

A potent greenhouse gas, trifluoromethyl sulfur pentafluoride (SF5CF3), has been discovered in the Earth's upper atmosphere. There are no known natural sources of SF5CF3, and it has been reported that high-energy electron irradiation (5keV) of condensed mixtures of SF6 and CF4 forms SF5CF3. This paper focuses on a search for the electron-induced formation of SF5CF3 at low electron energies and for the mechanism of formation of SF5CF3. Temperature-programmed desorption (TPD) and electron-stimulated desorption (ESD) are used to search for products formed under electron irradiation of ultrathin condensed films (∼3 ML) of SF6 and CF4. The major evidence for the formation of SF5CF3 via irradiation is the observation in ESD of ionic fragments containing S−C bonds, which are also seen in the mass spectra of SF5CF3. The maximum yield of SF5CF3 products in the condensed film is induced by ∼8 eV electron irradiation; the mechanism is associated with low-energy dissociative electron attachment (DEA) of SF6 and CF4 f...