Structure and vibrational spectra of p-methylaniline:: Hartree-Fock, MP2 and density functional theory studies

The FT-IR and FT-Raman spectra of p-methylaniline (pMA) have been recorded. Optimized molecular structures and normal vibrations of pMA have been obtained from the HF, MP2 and DFT-B3LYP methods implementing the 6-31G* and 6-31G** basis sets. Scale factors, which bring computational frequencies in closer agreement with the experimental data, have been calculated for predominant vibrational motions of the normal modes at each level considered. All observed harmonic IR and Raman bands of pMA have been assigned in the frameworks of the calculations. The assignments have been compared each other and with the 30 benzene-like modes. The effects of the methyl and amino substituents on vibrational frequencies have been investigated. The applicability limits of HF, MP2 and DFT-B3LYP methods have been discussed. The DFT-B3LYP method has been found very promising for vibrational spectral analyses. (C) 2003 Elsevier B.V. All rights reserved.