Searching for Large Molecules
Large carbon molecules play an important role in interstellar chemistry, building a bridge between small gas-phase species and grains. Many of the large carbon molecules, in particular the pure carbon chains of moderate length and the polycyclic aromatic hydrocarbons (hereafter PAHs), have no permanent dipole moment and cannot be observed by their pure rotational spectra. However, they have low-frequency bending rovibrational transitions in the far-IR to submillimeter range which are very specific to the identity of their carbon skeleton. The program will use the opening of this spectral range as an opportunity for Herschel, with HIFI and PACS, to detect and – more importantly – identify them. The observations for this program will be defined once the spectral scan data has been obtained. Christine Joblin is the coordinator for this subprogram.