2000A&A...353.1101B

We present millimetre and submillimetre observations of comet C/1995 O1 (Hale-Bopp) undertaken near perihelion with the Caltech Submillimeter Observatory and the 30-m telescope and Plateau-de-Bure interferometer of the Institut de Radioastronomie Millimetrique. From a spectral molecular survey, six new cometary molecular species have been identified for the first time in a comet: SO, SO₂, HC₃N, NH₂CHO, HCOOH, and HCOOCH₃. Relative abundances with respect to water are 0.3% (SO), 0.2% (SO₂), 0.02% (HC₃N), 0.01-0.02% (NH₂CHO), 0.09% (HCOOH), and 0.08% (HCOOCH₃). Several rotational transitions of OCS and HNCO, whose first identifications were made previously in comet C/1996 B2 (Hyakutake), have also been detected, confirming that these molecular species are ubiquitous compounds of cometary atmospheres. Inferred abundances of OCS and HNCO relative to water in comet Hale-Bopp are 0.4% and 0.1%, respectively. During this observational campaign, we also observed rotational lines of HCN, HNC, CH₃CN, CO, CH₃OH, H₂CO, H₂S, and CS. In combination with results of other observations, a comprehensive view of the volatile composition of the coma of comet Hale-Bopp is obtained. A quantitative comparison shows that chemical abundances in comet Hale-Bopp parallel those inferred in interstellar ices, hot molecular cores and bipolar flows around protostars. This suggests that the processes at work in the interstellar medium, in particular grain surface chemistry, played a major role in the formation of cometary ices. It supports models in which cometary volatiles formed in the interstellar medium and suffered little processing in the Solar Nebula.