Theoretical Raman and infrared spectra, and vibrational assignment for para-halogenoanilines: DFT study

The theoretical IR and Raman spectra of para-halogenoanilines, 4-XC6H4NH2 (X = F, Cl and Br) were calculated by using the density functional B3LYP method with the 6-311++G(df,pd) basis set. The theoretical spectra show very good agreement with experiment. The rigorous normal coordinate analyses have been performed, and the detailed vibrational assignment has been made on the basis of the calculated potential energy distributions (PEDs). Several ambiguities and contradictions in the previously reported vibrational assignments have been clarified. The “marker bands” and the effects of the halogen substituent on the characteristic aniline bands in the IR and Raman spectra are discussed.