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

Abstract

Naphthalene cations (C 10H 8 +) were produced in a slit jet coupled with an electronic discharge, and cavity ring down was used to obtain its absorption spectrum in the region 645–680 nm. Two of the strongest C 10H 8 + bands previously 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). This work opens the way for a direct comparison of laboratory PAH spectra with the diffuse interstellar bands (DIB), the origin of which still constitutes an open problem in astrophysics.