1999A&A...341..882W

We report IRAM 30-m observations of vibrationally excited rotational transitions of HC₃N toward a sample of six ultra-compact HII regions. In addition, Effelsberg 100-m and Plateau de Bure Interferometer measurements were conducted toward the region G10.47+0.03. We detected the v₇=1 state of cyanoacetylene toward all six regions and the v₆=1 line toward five of them. Toward G10.47+0.03, we detected lines from 11 different vibrationally excited states with excitation energies up to 1600K above ground. Of these, six are first detections. We also have detected several transitions of ¹³C substituted cyanoacetylene in the v₆=1, v₇=1, and v₇=2 states and provide improved rest frequencies for several of these. The population distribution of the vibrationally excited HC₃N molecules is analyzed and it is concluded that our results are consistent with thermalised level populations at a temperature of 270K. From the interferometer results we find the source of HC₃N emission to be coincident with NH₃(4,4) and CH₃CN emission within the positional error of 1". In an appendix, we report the first astronomical detection of lines from vibrationally excited HNCO in G10.47+0.03.