The optimized geometries, vibrational force fields and infrared intensities of FC(O) NCS were calculated by HF, MP2, DFT(B3LYP) methods with 6-31G* basis set. The theoretical force field of B2LYP/ 6-31G* were scaled using the scaled quantum mechanical force field method of Pulay. The average deviations between the experimental and computed frequencies are 10 and 13 cm^-^1 for the cis - and trans- isomers of FC(O)NCS, respectively. The assignments of the fundamentals for two rotational conformers of this molecule were also performed according to the potential energy distribution and the infrared intensities.

Key words: ISOTHIOCYANATE, CARBONYL COMPOUNDS, NORMAL COORDINATE ANALYSIS, FLUORINE COMPOUNDS, INFRARED SPECTROPHOTOMETRY