Accurate laboratory rest frequencies of vibrationally excited COup to v= 3 and up to 2 THz

摘要

Aims. Astronomical observations of (sub)millimeter wavelength pure rotational emission lines of the second most abundant moleculein the Universe, CO, hold the promise of probing regions of high temperature and density in the innermost parts of circumstellarenvelopes.Methods. The rotational spectrum of vibrationally excited CO up to u = 3 has been measured in the laboratory between 220 and1940 GHz with relative accuracies up to 5.2 x 10-9, 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 thesextic distortion term H was determined quite well for u = 1 while reasonable estimates of H were obtained for u = 2 and 3.Conclusions. The present data set allows for the prediction of accurate rest frequencies of vibrationally excited CO well beyond2 THz.