Accurate rest frequencies for the submillimetre-wave lines of CO in ground and vibrationally excited states below 400 cm ^*

Dipartimento di Chimica “G. Ciamician”, via F. Selmi 2, 40126 Bologna, Italy e-mail: [luca.bizzocchi;claudio.degliesposti;luca.dore]@unibo.it

Received: 14 July 2008
Accepted: 18 September 2008

Abstract

The submillimetre-wave spectrum of C₃O () 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 307–740 GHz 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 , and for its overtones and 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.