Theoretical and Experimental (400-10 000 cm-1) Study of the Vibrational Spectrum of Pentachlorophenol.

Geometric and vibrational spectroscopic data (bond distances and angles, vibrational frequencies, infrared intensities) of pentachlorophenol-OH (PCP-OH) and pentachlorophenol-OD (PCP-OD) are calculated by density functional theory (B3LYP) using the 6-311G(d, p) basis set. Except for the vibrations involving the OH bond, the agreement between the experimental and calculated fundamental frequencies between 3600 and 400 cm-1 is very good. The theoretical method failed, however, to reproduce quantitatively the experimental intensities. The infrared spectra between 3600 and 10 000 cm-1 are studied, and the overtones or combination bands are assigned by comparing the spectra of PCP-OH and PCP-OD. The difference between the experimental and theoretical frequencies of the nu(OH) and nu(OD) frequencies can be mainly accounted for by the neglect of the anharmonicities of these vibrations in calculations. The binary or ternary combinations characterized by the highest coupling constants and the highest intensities are those involving the nu(OH), delta(OH), gamma(OH), and nu(C-O) vibrations. Copyright 1999 Academic Press.