Infrared and Raman spectra of 4-(dimethylamino)benzonitrile and isotopomers in the ground state and vibrational analysis Original Research Article

Vibrational analysis of 4-(dimethylamino)benzonitrile (DMABN) has been performed. Infrared and Raman spectra of DMABN and its four different isotope-labeled species have been recorded. Assignments of the vibrational bands are given on the basis of normal coordinate calculation on an empirical force field and of the Hartree–Fock and the density functional calculations. Most of the vibrational bands observed have been successfully assigned, and the isotope shifts are reasonably explained. It is clearly demonstrated from the measurements on the isotopomers that assignments of some bands in the literature are not correct. The characteristics of the empirical and the quantum-chemical force fields are compared. It has been found that the strong interaction between the dimethylamino group and the benzene ring is directly reflected in the force field.