The vacuum-UV absorption spectrum of SF5CF3; implications for its lifetime in the earth’s atmosphere

Using vacuum-UV radiation from a synchrotron source, the absorption spectrum of SF\(_5\)CF\(_3\) has been measured in the range 50-150 nm at a resolution of 0.12 nm. The cross section at the Lyman-\(\alpha\) wavelength of 121.6 nm is 1.5 \(\pm\) 0.3 x 10\(^{-17}\) cm\(^2\) molecule\(^{-1}\). The loss of SF\(_5\)CF\(_3\) on a molecular basis from the earth’s atmosphere is dominated, not by photon-induced dissociation, but by electron attachment in the mesosphere above 60 km, yielding SF\(_5^-\). The lifetime of SF\(_5\)CF\(_3\) in the earth’s atmosphere, however, is determined primarily by the meterological conditions that transport it from the earth’s surface to the mesosphere, and not by processes that occur in that region. By comparison with data for SF\(_6\), a lifetime of ca. 1000 years for SF\(_5\)CF\(_3\) is estimated.