Rotational Spectra of Sulfur-Carbon Chains. I. The Radicals C and 4S, C5S, C6S, C7S, C8S, C9S

The linear carbon-chain radicals C6S, C7S, C8S, and C9S have been detected in a supersonic molecular beam by Fourier transform microwave spectroscopy, and measurements of the previously studied chains C4S and C5S have been extended using the same technique. The electronic ground state, as predicted, is found to be a triplet for those with an even number of carbon atoms and a singlet for those with an odd number. The microwave spectra of all six chains have been fully characterized, and spectroscopic constants, including fine-structure constants where applicable, have been determined to high precision. Transitions from the J=N and J=N-1 fine-structure levels of C4S have been detected for the first time, and the lengths of the individual bonds of C5S have been determined from its isotopic species. The carbon-sulfur chains here are all highly polar, calculated to possess dipole moments in the 4-7 D range; all are plausible candidates for astronomical detection. The spectroscopic constants determined from this work allow transitions up to 40 GHz to be calculated with an uncertainty of less than 1 km s -1 for each chain. Subject headings : ISM: molecules -- line : identiÐcation -- molecular data -- molecular processes -- radio lines : ISM