Infrared cavity ringdown spectroscopy of jet-cooled polycylic aromatic hydrocarbons

Infrared absorption spectra of the CH stretching region were observed for naphthalene, anthracene, phenanthrene, pyrene, and perylene using a heated, supersonic, slit-jet source and cavity ringdown spectroscopy. Band positions and intensities recorded with 0.2-cm(-1) resolution were compared with previous gas phase and argon matrix isolation experiments, as well as theoretical calculations. The largest matrix shift in the absorption maximum (-7.4 cm(-1)) was observed for anthracene, with all others shifted by 30 cm(-1) or less. Special features in the supersonic jet spectrum were generally narrower than those observed in the Ar matrix, with the largest matrix broadening found for the perylene (80% increase). Low number densities observed for the larger polycyclic aromatic hydrocarbons (PAHs) suggest that the lower vapor pressure of PAHs with catacondensed four-membered rings and with five-membered rings other than perylene will not be detectable using our current configuration.