Density functional and experimental studies on the FT-IR and FT-Raman spectra and structure of benzoic acid and 3,5-dichloro salicylic acid

FT-IR and FT-Raman spectra of benzoic acid (BA) and 3,5-dichloro salicylic acid (SA) have been recorded in the regions of 4000-400 and 4000-50 cm(-1) respectively. The spectra were interpreted with the aid of normal coordinate analysis following the full structure optimizations and force field calculations based on density functional theory (DFT) using standard B3LYP6-31G** method and basis set combinations. The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compounds. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Copyright (C) 2008 John Wiley & Sons, Ltd.