Formation of Carbonaceous Molecules in the ISM

Among the more than 150 molecules detected in space highly reactive, carbonaceous species such as light carbon hydrides CH, CH_2, as well as small carbon chain molecules, C_nH_m (n = 3, 4, 5, ... and m=0,1,2), are prominent. The lowest bending modes of many carbon chain molecules lie in the Terahertz frequency region. Due to absence of a permanent dipole moment, centro-symmetric linear molecules of the form C_n, HC_nH, or NC_nN have no pure rotational spectra. They can only be detected by their ro-vibrational spectra which all lie in the Terahertz range, unless suitable background sources happen to be available for optical/IR absorption studies. Laboratory investigations therefore aim for precise spectral data of carbonaceous molecules to foster future astrophysical observations with telescopes onboard the Herschel satellite and SOFIA as well as high altitude observatories like APEX and ALMA. For laboratory investigations the combination of supersonic jet apparatuses with laser ablation techniques and electrical discharge sources allow the production of reactive and short lived molecules at low rotational temperatures. Rotationally resolved spectra of carbonaceous molecules in supersonic jets are studied by means of mm- to submm-wavelength and mid-Infrared spectroscopy. Laboratory data of linear triatomic carbon (C_3) led to its recent observation of the sight-lines to the star forming regions W31C and W49N. Recent progress on laboratory investigation will be presented.