Predicted specific heat behaviour of the polychlorinated dibenzofuran family from DFT analysis

The need for accurate thermodynamic data for the polychlorinated dibenzofuran family of isomers arises from the continued interest in the prediction of relative populations of these, and the lack of experimental data justifies the need for the calculation of these at a sufficiently accurate level. In order to add to the existing databases, specific heats have been calculated for the full 135 isomer set of PCDFs using B3LYP density functional theory calculations at the 6-31G(d) and 6-311+G(3df,p) basis set levels. These are calculated for temperatures up to 800 K as well as the accompanying heats of formation and entropies at standard conditions. Knowledge of the specific heats up to this temperature gives greater confidence in the calculation of free energy values in the temperature ranges known to be important for PCDF formation and transformation. It is shown that a reduced set of quadratic functions can be used to represent the Cp values for the eight isomer groups of the PCDF family and the methodology used is shown to predict the Cp and entropy values with good accuracy for a number of other molecules for which experimental values are known.