N and D is used in the identification of vibration modes. Innonhydroge-nated materials containing low nitrogen concentration ~<20 at. %!, the ir and Raman spectra are not equiva-lent. Above this concentration ~up to ;30 at. %!, the spectra became very similar to each other. On thecontrary, for a suitable hydrogen content the spectra are quite similar, independently of the range of nitrogenconcentrations studied. Quantum chemical Parametric Method 3 calculations are performed to obtain thefrequencies and intensities of the ir active vibrations of organic molecules and large carbon-nitrogen clusters.These results are used to help in the identification of the features observed in the ir spectra. The importance ofboth the promotion of bond dipoles and symmetry breaking by nitrogen in the ir spectra is established.I. INTRODUCTION