Abstract: The harmonic force field and the vibrational spectrum of nitramide were calculated by using the ab initio gradient program TEXA Sat the Hartree-Fock level with a 4-21G basis set. The directly computed theoretical harmonic force field was scaled by using empirical scale factors which are transferred from other molecules and provided an a priori prediction of fundamental frequencies and intensities. The average deviations between predicted vibrational frequencies of nitramide and experimental IRspectrum in an argon matrix are 63 cm^-1for symmetric vibrations and 41 cm^-1for antisymmetric modes. Anew set of scale factors was optimized in this paper. These scale factors reduced the average deviations to 2. 3 cm^-1for symmetric modes and 0. 8 cm^-1for antisymmetric ones. The vibrational spectra of three isotopic derivatives of nitramide were predicted by using the force field resulted from the optimized set of scale factors, which are in good agreement with their experimental data in an argon matrix.

Key words: Nitramide, Harmonic force field, Vibrational spectrum