Cavity ring-down spectroscopy of carbon-containing molecules

Among other carbonaceous species, polycyclic aromatic hydrocarbons (PAHs) are of relevance for astrophysics. It is expected that they are present in the interstellar medium and they are considered as possible carriers of the diffuse interstellar bands. To prove this, absorption spectra of PAHs under conditions similar to those met in the interstellar medium should be obtained. We report here the application of cavity ring-down laser absorption spectroscopy to neutral PAHs, namely anthracene and pyrene, cooled in a supersonic jet. The absorption spectra corresponding to the S-1(0) <-- S-0(0) transition of anthracene near 361 nm and to the S-2(1,0) <-- S-0(0) transitions of pyrene around 321 nm and 316 nm have been studied. The results are similar to the excitation spectra previously reported in the literature.