CF3SF5 : a ‘super’ greenhouse gas

One molecule of the anthropogenic pollutant trifluoromethyl sulphur pentafluoride (CF\(_3\)SF\(_5\)), an adduct of the CF\(_3\) and SF\(_5\) free radicals, causes more global warming than one molecule of any other greenhouse gas yet detected in the Earth’s atmosphere. That is, 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\(_6\). First, the greenhouse effect is described, the properties of a molecule that cause it to be a significant greenhouse gas, and therefore the contributions that physical chemistry can make to an improved understanding of the effect. Second, the chemistry of (CF\(_3\)SF\(_5\)), first discovered in the atmosphere in 2000, is taken as a case study. Experiments using tunable vacuum-UV radiation, electrons and small cations have determined some of the relevant physical properties of this molecule, including the strength of the (CF\(_3\)-SF\(_5\)) covalent bond. The main sink route to remove (CF\(_3\)SF\(_5\)) from the earth’s atmosphere is low-energy electron attachment in the mesosphere. Third, it is shown how such data are important inputs to determine the lifetime of this pollutant, ca. 1000 years, in the atmosphere. Finally, the generic lessons that can be learnt from the study of such long-lived greenhouse gases are described.