Theoretical model for infrared spectra of hydrogen- bonded 2,4-dithiouracil crystal

Theoretical model describing infrared spectra of the N-H(D) stretching bands in 2,4-dithiouracil and its deuterated derivative is presented. The model takes into account anharmonic coupling between the high-frequency NH(D) stretching and the low-frequency N...S stretching vibrations, resonance interaction between two equivalent hydrogen bonds in the dimer, anharmonicity of the potentials for the low-frequency vibrations in the ground and excited state of the N-H(D) stretching mode, Fermi resonance between the N-H(D) stretching and the first overtone of the NH(D) bending vibrations, and electrical anharmonicity.