Theoretical studies on vibrational spectra of FC(O)NCS

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 Geld of B3LYP/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.