Using vacuum-UV radiation from a synchrotron source, the absorption spectrum of SF5CF3 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 +/- 0.3 x 10(-17) cm(2) molecule(-1). The loss of SF5CF3 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 SF5-. The lifetime of SF5CF3 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 SF6, a lifetime of ca. 1000 years for SF5CF3 is estimated. (C) 2002 Elsevier Science B.V. All rights reserved.