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