title: Chemistry in cometary comae.
abstract: Significant gas-phase chemistry occurs in the comae of bright comets, as is demonstrated here for the case of Comet Hale-Bopp. The abundance ratio of the two isomers, hydrogen cyanide and hydrogen isocyanide, is shown to vary with heliocentric distance in a way that is consistent with production of HNC by ion-molecule chemistry initiated by the photoionization of water. Likewise, the first maps of emission from HCO+ show an abundance and an extended distribution that are consistent with the same chemical model.
authors.affiliation: Five College Radio Astronomy Observatory, University of Massachusetts, Amherst 01003, USA.
authors.forename: W M
authors.initials: WM
authors.lastname: Irvine
authors.forename: J E
authors.initials: JE
authors.lastname: Dickens
authors.forename: A J
authors.initials: AJ
authors.lastname: Lovell
authors.forename: F P
authors.initials: FP
authors.lastname: Schloerb
authors.forename: M
authors.initials: M
authors.lastname: Senay
authors.forename: E A
authors.initials: EA
authors.lastname: Bergin
authors.forename: D
authors.initials: D
authors.lastname: Jewitt
authors.forename: H E
authors.initials: HE
authors.lastname: Matthews
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003485:Cyanates / Q000032:analysis* / Q000737:chemistry; D005740:Gases; D006856:Hydrogen Cyanide / Q000032:analysis* / Q000737:chemistry; D019110:Meteoroids
chemical_list: D003485:Cyanates; D005740:Gases; D006856:Hydrogen Cyanide; C005057:isocyanic acid