Accurate scaling of the vibrational spectra of aniline and several derivatives

The structure of aniline was studied by quantum chemical methods. Complete geometry optimization of the minimum energy structure and of the transition states for internal rotation and inversion of the amino group was carried out using several levels. The performance of the different methods in calculating and describing the vibrational wavenumbers of aniline was determined. The normal modes were characterized by the magnitude and direction of the displacement vectors. Three procedures were used to obtain the scaled wavenumbers, two of them new, using specific scale factors and scaling equations from benzene molecule. The errors obtained were compared with those calculated through other standard procedures. A reassignment of several bands was made. A comparison of the cost/effective method and procedure of scaling was carried out. Specific scale factors and scale equations were determined for the amino group to be used in large aromatic amines. (C) 2002 Elsevier Science B.V. All rights reserved.