Organic synthesis in the coma of Comet Hale-Bopp?

Several organic molecules have now been detected in the coma of Hale-Bopp. These species may either emanate from the nucleus, or, as has been suggeste d by Bockelee-Morvan et al., could be synthesized in the coma. We have mode lled the gas phase chemistry which occurred in the coma of Hale-Bopp, conce ntrating on the observed organic molecules HCOOH, HCOOCH3, HC3N and CH3CN. We find that gas phase chemical reactions are unable to synthesize the obse rved abundances of these molecules, so all these species are most probably present in the nuclear ice. We briefly discuss the implications of this res ult for the connection between cometary and interstellar ices.