Theoretical and spectroscopic study of hydrogen bond vibrations in imidazole and its deuterated derivative

Theoretical simulation of the bandshape and fine structure of the N-H(D) stretching band is presented for imidazole and its deuterated derivative taking into account adiabatic coupling between the high-frequency N-H(D) stretching and the low-frequency N center dot center dot center dot N stretching vibrations, 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 electric anharmonicity. The vibrational potential functions describing N-H and N center dot center dot center dot N stretching modes have been obtained from ab initio calculations. The effect of deuteration has been successfully reproduced by our model calculations. Infrared, far-infrared, Raman and low-frequency Raman spectra of the polycrystalline imidazole have been recorded. The geometry and experimental frequencies are compared with the results of harmonic MP2/6-311++G** and anharmonic B3LYP/6-311++G** calculations. (C) 2010 Elsevier B. V. All rights reserved.