Thermodynamic properties of polycyclic aromatic hydrocarbons in the subcooled liquid state

A knowledge of the solution behavior of polycyclic aromatic hydrocarbons (P AHs) at ambient temperatures is required for predictions of their fate in t he environment. Unsubstituted PAHs are crystalline at ambient temperatures, but their behavior in solution depends on the properties of the hypothetic al subcooled liquid state, and these properties must be estimated. Enthalpi es, entropies, and Gibbs free energies of fifteen PAHs in the subcooled liq uid state are calculated using available sublimation, melting, and heat cap acity data. Because PAH melting points are as much as 250 K above ambient t emperatures, heat capacity corrections can be important for the accurate ex trapolation of thermodynamic data to the subcooled liquid slate. For exampl e, subcooled liquid vapor pressures, p(l), at 298 K calculated without heat capacity corrections are up to 6 times higher than those estimated with he at capacity corrections. Calculated values for p(l) are expressed as log p( l) =(.) (.)A/T + B and used to develop a group contribution method for the calculation of p(l) for other unsubstituted PAHs.