The HNC/HCN ratio in comets.
The abundance ratio of the isomers HCN and HNC has been investigated in comet Hale-Bopp (C/1995 O1) through observations of the J = 4-3 rotational transitions of both species for heliocentric distances 0.93 < r < 3 AU, both pre- and post-perihelion. After correcting for the optical depth of the stronger HCN line, we find that the column density ratio of HNC/HCN in our telescope beam increases significantly as the comet approaches the Sun. We compare this behavior to that predicted from an ion-molecule chemical model and conclude that the HNC is produced in significant measure by chemical processes in the coma; i.e., for comet Hale-Bopp, HNC is not a parent molecule sublimating from the nucleus.
Irvine
W M
WM
Five College Radio Astronomy Observatory, University of Massachusetts, Amherst 01003, USA.
Dickens
J E
JE
Lovell
A J
AJ
Schloerb
F P
FP
Senay
M
M
Bergin
E A
EA
Jewitt
D
D
Matthews
H E
HE
D055580:Astronomical Phenomena; D001256:Astronomy; D003486:Cyanides / Q000032:analysis* / Q000737:chemistry; D005118:Extraterrestrial Environment; D006856:Hydrogen Cyanide / Q000032:analysis* / Q000737:chemistry; D007536:Isomerism; D019110:Meteoroids; D008956:Models, Chemical; D010777:Photochemistry; D016082:Solar System
D003486:Cyanides; D006856:Hydrogen Cyanide