Supercooled liquid vapor pressures of the polycyclic aromatic hydrocarbons

The vapor pressure of the supercooled liquid (PL) for 35 unsubstituted and alkylated polycyclic aromatic hydrocarbons (PAHs) was determined as a function of temperature using a gas chromatographic retention time technique. Pyrene and 1,2-benzanthracene, two compounds with well-established temperature-dependent vapor pressures, served as standard reference compounds. The method was calibrated with nine PAHs for which the vapor pressures at 25 degreesC are known from measurements relying on gas saturation and gas effusion techniques. Enthalpies of vaporization Delta(vap)H were also determined. The P-L data were evaluated by comparison with several sets of published data and found to be reliable. For most of the investigated PAHs, a strong linear relationship between 109 PL and molecular mass exists, ranging over more than 9 orders of magnitude. However, PAHs with bulky substituents, such as phenyl- and tertbutyl-groups, have a higher vapor pressure than would be expected on the basis of molecular mass, presumably because of the lack of molecular planarity.