LASER-INDUCED FLUORESCENCE SPECTROSCOPY OF JET-COOLED MOLECULAR-SPECIES - A TOOL TO IDENTIFY DIFFUSE INTERSTELLAR BAND CARRIERS

We present the first results of an experimental method (jet expansion followed by laser induced fluorescence) that collects absorption spect ra of cold, gas-phase isolated species. This method, closely simulatin g interstellar conditions, is a powerful tool to assert diffuse inters tellar bands (DIB) identification. It only requires the species studie d to be fluorescent. This latter condition is fulfilled for some DIB c arriers as shown recently. Stimulated by the recent detection in rare- gas matrices of its fluorescence, we focus on the perylene cation. Thi s molecule pertains to a family (the polycyclic aromatic hydrocarbons or PAHs) whose ions or radicals are potential DIB carriers. We failed to detect the fluorescence observed in rare-gas matrix. Rather, we obs erved a photofragmentation process leading to the C-2 molecule. We thu s obtained the absorption spectrum of a PAH radical of size comparable to its parent molecule, perylene. From a comparison with the DIB spec trum, we find that rotationally broadened bands of PAH radicals may ex plain the profile of broad DIBs, or regularly spaced DIBs sequences.