Anharmonic analysis of the vibrational states of pyrimidine by the density functional method

The quartic force field of pyrimidine is calculated in the approximation of the hybrid density functional B3LYP/6-31G(d). On the basis of this force field, the IR spectrum of pyrimidine in the range 250–3800 cm^?1 is interpreted. The Darling-Dennison and Fermi resonances are taken into account and their spectral manifestations are analyzed. A combined method for the anharmonic analysis of the vibrational states of polyatomic molecules that employs the theoretical anharmonicity constants and experimental frequencies is proposed. The method ensures a higher prediction accuracy.