Thermodynamic properties of dibenzo-p-dioxin, dibenzofuran, and their polychlorinated derivatives in the gaseous and condensed phases. 1. Thermodynamic properties of gaseous compounds

Gas-phase thermodynamic properties (enthalpy of formation, entropy, and hea t capacity) are estimated for dibenzo-p-dioxin (DD), dibenzofuran (DF), 75 possible isomers of polychlorinated dibenzo-p-dioxins (PCDDs), and 135 of p olychlorinated dibenzofurans (PCDFs). To estimate the enthalpy of formation values, the difference method is used that is completely consistent with t he group additivity approach. Entropies and heat capacities are calculated by statistical thermodynamics using evaluated structural parameters and vib rational frequencies. Normal coordinate analysis is carried out for all iso mers of PCDDs and PCDFs by transferring the force constants from polycyclic aromatic hydrocarbons, dibenzofuran, and chlorinated benzenes. The group a dditivity scheme with 10 parameters is developed to approximate calculated thermodynamic properties. Results obtained in this work are compared with p ublished experimental and theoretical data.