Structural and vibrational properties of pentabromophenol and pentafluorophenol: A spectroscopic investigation using density functional theory

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Fourier Transform Raman and Fourier Transform infrared spectra were measured in the spectral range 3500-100 cm−1 and 4000-400 cm−1, respectively, for Pentabromophenol (PBP) and Pentafluorophenol (PFP). Torsional potentials, optimized structure parameters, harmonic vibrational frequencies, general valance force field, potential energy distribution (PED), along with infrared and Raman intensities were evaluated, for PBP and PFP. DFT was used in conjunction with B3LYP functional with 6–311++G (d,p) basis set, for the computations. Scaling process was employed to get a better fit between the measured and computed frequencies. The rms error between them was 9.7 and 7.0 cm−1, for PBP and PFP, respectively. Unambiguous vibrational assignments were arrived at by using PED and eigenvectors. In order to substantiate the existence of inter-molecular hydrogen bond in these molecules geometry optimization was made for dimers of PBP and PFP, at the same level of theory as used for the monomers.