Jet-discharge cavity ring-down spectroscopy of ionized polycyclic aromatichydrocarbons: progress in testing the PAH hypothesis for the diffuse interstellar band problem

Naphthalene cations (C10H8+ were produced in a slit jet coupled with an ele ctronic discharge, and cavity ring down was used to obtain its absorption s pectrum in the region 645-680 nm. Two of the strongest C10H8+ bands previou sly characterized by matrix isolation spectroscopy were found, both with a fractional blue shift of about 0.5%. This is the first gas-phase electronic absorption spectrum of an ionized polycyclic aromatic hydrocarbon (PAH). T his work opens the way for a direct comparison of laboratory PAH spectra wi th the diffuse interstellar bands (DIB), the origin of which still constitu tes an open problem in astrophysics. (C) 1999 Elsevier Science B.V. All rig hts reserved.