Theoretical and spectroscopic study of infrared spectra of hydrogen-bonded 1-methyluracil crystal and its deuterated derivative

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Abstract
Theoretical simulation of the band shape and fine structure of the N–H(D) stretching band is presented for 1-methyluracil and its deuterated derivative taking into account anharmonic coupling between the high-frequency N–H(D) stretching and the low-frequency N⋯O 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 N–H(D) bending vibrations, and electrical anharmonicity. The effect of deuteration has been successfully reproduced by our model calculations. Infrared, far-infrared, Raman, and low-frequency Raman spectra of the polycrystalline 1-methyluracil have been recorded. The geometry and experimental frequencies are compared with the results of harmonic and anharmonic B 3 LYP ∕ 6 - 311 + + G * * calculations.