The formation of SF5CF3(X(1)A'), through the radical-radical recombination of SF5(X(2)A(1)) and CF3(X(2)A(1)), was observed for the first time in low-temperature sulfur hexafluoride-carbon tetrafluoride matrices at 12 K via infrared spectroscopy upon irradiation of the ices with energetic electrons. The nu(1) fundamentals of the SF5(X(2)A(1)) and CF3(X(2)A(1)) radicals were monitored at 857 and 1110 cm(-1), respectively; the newly formed trifluoromethyl sulfur pentafluoride molecule, SF5CF3(X(1)A'), was detected via its absorptions at 846 and 1160 cm(-1). This formation mechanism suggests that a source for this potentially dangerous greenhouse gas might be the recombination of SF5(X(2)A(1)) and CF3(X(2)A(1)) radicals on aerosol particles in the terrestrial atmosphere.