The vibrational spectra of 3, 3", 5, 5"-tetrachloro-p-terphenyl, 2,2", 4,4"-tetrachloro-p-terphenyl, 2', 3, 3", 5, 5"-pentachloro-p-terphenyl and 3,3",5,5"-tetrachloro-m-terphenyl have been calculated using hybrid density functional theory (B3LYP/6-31G*) and a single scaling factor. The calculated spectra have been compared to experimental gas phase spectra. The agreement between theoretical and experimental spectra is excellent and allows the identification of an unknown congener just by pattern recognition. Differences of individual C-Cl bond strengths were studied by compliance matrix calculations. (C) 2002 Elsevier Science B.V. All rights reserved.