2008A&A...492..875B

The submillimetre-wave spectrum of C₃O (X¹Σ⁺) has been investigated in the laboratory using a source-modulation microwave spectrometer equipped with a gas-phase flow pyrolysis system for the production of unstable chemical species. C₃O was produced by thermal decomposition of fumaryl chloride at 900 °C. Thirty-seven new rotational transitions were observed in the frequency range 307-740GHz for the ground vibrational state, reaching a J quantum number as high as 76. Additionally, new millimetre-wave and submillimetre-wave lines were recorded for the bending fundamental v₅=1, and for its overtones v₅=2 and v₅=3 whose rotational spectra have been identified for the first time. The new laboratory measurements provide much improved rest frequencies in the submillimetre spectral region for the ground state spectra of C₃O, and for the first levels of its low-energy v₅ vibrational ladder, useful for the radioastronomical identification of their rotational lines in the ISM.