Absorption Spectroscopy of Astrophysically Relevant Molecules in Supersonic Jets

The jet‐cooled ultraviolet absorption spectra of various polycyclic aromatic hydrocarbons (PAHs) have been measured by cavity ring‐down laser absorption spectroscopy. The number of aromatic rings in the molecules studied varied from three (anthracene and phenanthrene) to six (benzo[g,h,i]perylene). None of the spectra comply with astronomical observations. In order to derive maximum column densities of the respective molecules in the astrophysical objects, their oscillator strengths have been determined by comparing the jet spectra with Ne matrix spectra also measured in our laboratory and with calibrated solution spectra. The paper gives an overview of the electronic spectra measured so far in our group, discusses a typical example (perylene) and some pecularities of PAH spectra, describes the procedure how the jet spectra can be calibrated to present absolute absorption cross sections, and concludes with a perspective for finding specific PAHs in interstellar and circumstellar clouds.