Moller-Plesset (MP) perturbation theory and density functional theory (DFT) were used to examine the structure and bonding of trifluoromethyl sulfurpentafluoride, SF5CF3, and the corresponding anion, SF5CF3-. The structural parameters, charge analysis, and energetics are all consistent with the anion having ion-dipole character (i.e., SF5--CF3). Results from G2(MP2) theory yield a neutral D-298(0)(SF5-CF3)=301 kJ mol-1 (3.12 eV), anion D-298(0)(SF5--CF3)=21.5 kJ mol(-1) (0.22 eV), EA(SF5CF3)=119 kJ mol(-1) (1.24 eV), Delta(f)H(298)(0)(SF5CF3)=-1639 kJ mol(-1), and Delta(f)H(298)(SF5CF3-)=-1750 kJ mol(-1). The calculated value for the standard enthalpy of formation for SF5CF3 differs from the previous estimate by 78 kJ mol(-1). DFT was found to perform poorly for quantities related to the neutral SF5-CF3 bond. Calculations were also carried out for SF5, SF5-, CF3, and CF3- fragments, and both DFT and G2(MP2) methods performed well for these open-shell species. Rate constants for electron attachment to SF5CF3 were measured over the temperature range 296-563 K in 133 Pa helium gas using a flowing afterglow Langmuir probe apparatus. The 296 K rate constant is (8.6+/-2.2)x10(-8) cm(3) s(-1), which agrees within uncertainties with the estimate reported by Kennedy and Mayhew [Int. J. Mass Spectrom. 206, i-iv (2001)]. The only ionic product of attachment is SF5-. The temperature dependence of the electron attachment rate constant implies an activation energy of 25 meV. Implications of this work for estimating the atmospheric lifetime of SF5CF3 are discussed.