The IR and Raman spectra of the two molecules terephtalonitrile and terephtalonitrile-15N were recorded to permit the general assignment of the vibrational bands observed, in agreement with a D2h symmetry for these molecules. The general quadratic force field was calculated by the semi-empirical MINDO/3 method from an optimized geometry obtained by the same method. The resulting force field was refined by employing the experimental vibrational frequency data of the two molecules and those of terephtalonitrile-d4. The final differences between the calculated end experimentally observed frequencies for B2g and B3u terephtalonitrile species were within the range ± 0.1 cm−1.