The recently identified potent greenhouse gas, trifluoromethyl sulfur pentafluoride (SF5CF3), is studied using the hybrid density-functional method. Geometry optimization and frequency analysis show that the energy favorable torsional angle is zero. At room temperature, the CF3 group of the molecule is predicted to rotate freely along the F-S-C axis. An energy gap of 8.87 eV near the Fermi level indicates the absence of excited states within a few eV above the ground state. The vertical and adiabatic ion potentials and electronic affinities are obtained. Large values of the ion potentials suggest that the ionization of SF5CF3 is not favorable in energy. The experimental Fourier transform infrared spectrum of SF5CF3 in the 600-3800 cm(-1) region is well reproduced by our calculations. (C) 2002 Elsevier Science B.V. All rights reserved.