Interpretation of the vibrational spectra of nitramines on the basis ofab initio calculations

Abstract

It is shown that, unlike conventional methods of vibrational spectroscopy, the use ofab initia harmonic force fields, IR and Raman intensities, and depolarizations makes possible a rigorous interpretation of the experimental spectra of the simplest aliphatic nitramines (CH3)2NNO2, CH3NHNO2, H2NNO2, and their isotopomers. The scale factors, which were introduced for each compound to remove the systematic errors of the SCF MO LCAO calculation by fitting the parameters to the observed frequencies, were mutually adjusted during the solution of the inverse vibrational problem. The set of transferable scale factors established in this work can be used directly to analyze spectra of larger molecules. Some common patterns of the force fields and vibrational spectra of nitramines are discussed.