AB-INITIO STUDIES ON VIBRATIONAL-SPECTRA OF XSO2NCO (X=F, CL) - HARMONIC FORCE-FIELDS AND FREQUENCY ASSIGNMENTS

The harmonic vibrational force fields and the IR spectrum of XSO2NCO ( X = F, CL) molecules have been studied using ab initio HF/SCF method w ith the 6-31G basis set. The ab initio harmonic force fields are scal ed empirically using the scaled quantum mechanical (SQM) method of Pul ay. A set of scale factors are optimized by the least-squares fitting to the experimental frequencies of FSO2NCO and then are transferred to ClSO2NCO to give an a priori prediction of its fundamental frequencie s. The average deviations between the theoretical frequencies and the experimental values for FSO2NCO and ClSO2NCO are 3 and 5 cm(-1), respe ctively. The assignments of the fundamentals for these two molecules a re also made according to the potential energy distributions and the a b initio IR intensities.