General valence force fields for SF3CN and FS(O)CN are derived from vibrational data taken from the literature and from theoretical calculations. Gas phase electron diffraction;studies on both molecules yield the following geometric parameters (r(a) distances and angles with 3 sigma uncertainties). SF3CN : r(S-F-e) = 155.2(4) r(S-F-a) = 165.7(3), r(S-C)= 173.6(8), r(C=N) = 115.9(4) pm; angle(FaSFe) = 86.9(3), angle(FaSC) = 86.0(4) angle(FeSC) = 98.7(8), angle(FaSFa) = 169.0(6), angle(SCN) = 171(4)degrees. FS(O)CN : r(S-F) = 159.8(3), r(S=O) = 143.2(2), r(S-C) = 178.3(3), r(C=N) = 115.0(3) pm; angle(FSO) = 104.9(4), angle(FSC) = 93.9(4), angle(CSO) = 105.3(5), angle(SCN) = 176(4)degrees. These experimental results are compared to ab initio values (HF/3-21G*, HF/6-31G*, and MP2/6-31G*), and the bonding properties in these sulfur (IV) cyanides are discussed.