The absolute absorption cross-sections of a recently discovered atmospheric gas. SF5CF3, have been measured at He I (21.22 eV) and Ne I (16.64 and 16.82 eV) photon energies using a VUV discharge lamp and a double ion chamber method. Absorption cross-sections of (9.52 +/- 0.95) x 10(-17) cm(2) (He I) and (8.79 +/- 0.88) x 10(-17) cm(2) (Ne I) were obtained and compared with data from other studies. The consequences for the cross-section at the hydrogen Lyman-alpha energy (10.20 eV) are discussed. (C) 2003 Elsevier B.V. All rights reserved.