Accurate laboratory rest frequencies of vibrationally excited CO up to v = 3 and up to 2 THzR. Gendriesch1, F. Lewen1, G. Klapper1, K. M. Menten2, G. Winnewisser1, J. A. Coxon3, and H. S. P. Müller1
1 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
2 Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3 Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, B3H 4J3, Canada
Received 17 December 2008 / Accepted 6 February 2009
Aims. Astronomical observations of (sub)millimeter wavelength pure rotational emission lines of the second most abundant molecule in the Universe, CO, hold the promise of probing regions of high temperature and density in the innermost parts of circumstellar envelopes.
Methods. The rotational spectrum of vibrationally excited CO up to v = 3 has been measured in the laboratory between 220 and 1940 GHz with relative accuracies up to 5.210-9, corresponding to ~5 kHz near 1 THz.
Results. The rotational constant B and the quartic distortion parameter D have been determined with high accuracy and even the sextic distortion term H was determined quite well for v = 1 while reasonable estimates of H were obtained for v = 2 and 3.
Conclusions. The present data set allows for the prediction of accurate rest frequencies of vibrationally excited CO well beyond 2 THz.
Key words: molecular data -- methods: laboratory -- techniques: spectroscopic -- radio lines: ISM -- radio lines: stars -- ISM: molecules
© ESO 2009