Theoretical modeling of infrared spectra of benzoic acid and its deuterated derivative

Theoretical simulation of the ns stretching band is presented for benzoic acid and its OD derivative at 300 K. The simulation takes into account an adiabatic coupling between the high-frequency O–H(D) stretching and the low-frequency intermolecular O· · ·O stretching modes, linear and quadratic distortions of the potential energy for the low-frequency vibrations in the excited state of the O–H(D) stretching vibration, resonance interaction between the two hydrogen bonds in the dimer, and Fermi resonance between the fundamental n OH(D) stretching and the overtone of the d O–H(D) bending vibrations. Infrared, far-infarared, Raman and low-frequency Raman spectra of the polycrystalline benzoic acid and its deuterated form have been measured. The geometry and experimental frequencies are compared with the results of our B3LYP/6-311þþG** and B3LYP/cc-pVTZ calculations. q 2004 Elsevier B.V. All rights reserved.