CF3SiMe3 (Ruppert's reagent) has been investigated by gas phase electron diffraction, microwave spectroscopy and quantum chemical methods, deriving structural parameters and the barrier height for the methyl torsion. The bond length of the Si-CF3 bond, 1.941(3) angstrom is the longest Si-C bond observed so far in the gas phase. The V-3 barrier for the methyl group torsion (V-3 = 5.71 kJ/mol) is only slightly lower than barriers determined for other trimethylsilane compounds.