2001ApJS..134..311G

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.