The gas phase structure of N-(trifluoromethyl)iminosulphur dichloride, CF 3 N SCl 2 , has been determined by gas electron diffraction and quantum chemical calculations (HF/3-21G* and B3LYP/6-31G*). The CF 3 group staggers the S N bond and possesses a low barrier to internal rotation (V 0 =0.4(3) kcal mol - 1 ). The following important geometric parameters (r a values) were obtained: S N=1.513(6) 9, N-C=1.417(13) 9, S-Cl=2.077(7) 9, C-N S=130.8(21) o , N S-Cl=109.0(11) o and Cl-S-Cl=95.6(11) o . Both theoretical methods reproduce the experimental geometry satisfactorily with the exception of the C-N S angle and the S-Cl bond length. The HF approximation predicts the C-N S angle too large by 5 o and the hybrid method results in an S-Cl bond which is too long by 0.09 9.