Trifluoromethyl sulphur pentafluoride, SF5CF3: atmospheric chemistry and its environmental importance via the greenhouse effect

One molecule of SF\(_5\)CF\(_3\), an adduct of the SF\(_5\) and CF\(_3\) free radicals, causes more global warming than one molecule of any other greenhouse gas yet detected in the atmosphere, i.e. it has the highest per molecule radiative forcing of any greenhouse pollutant, and the value of its global warming potential is only exceeded by that of SF\(_6\). Using tunable vacuum-UV radiation from a synchrotron and coincidence spectroscopy, the strength of the central S-C bond in SF\(_5\)CF\(_3\) is determined to be 3.86 \(\pm\) 0.45 eV or 372 \(\pm\) 43 kJ mol\(^{-1}\), and this molecule is very unlikely to be removed from the earth’s atmosphere by UV photolysis in the stratosphere. Complementary laboratory-based experiments have shown that the main sink route of this greenhouse gas is low-energy electron attachment in the mesosphere, with Lyman-α photodissociation at 121.6 nm being only a minor channel. By comparison with data for SF\(_6\), the lifetime of SF\(_5\)CF\(_3\) in the earth’s atmosphere is estimated to be ca. 1000 years. The principal reason for the current low level of concern about the impact of SF\(_5\)CF\(_3\) on our environment is that the concentration levels are still very low, at the sub parts per trilllion level. The high growth rate of ca. 6% per annum, however, should cause concern for policymakers.