Hydrogen isocyanide, HNC: A key species in the chemistry of Titan's ionosphere?

Authors
Citation
S. Petrie, Hydrogen isocyanide, HNC: A key species in the chemistry of Titan's ionosphere?, ICARUS, 151(2), 2001, pp. 196-203
Citations number
68
Categorie Soggetti
Space Sciences
Journal title
ICARUS
ISSN journal
00191035 → ACNP
Volume
151
Issue
2
Year of publication
2001
Pages
196 - 203
Database
ISI
SICI code
0019-1035(200106)151:2<196:HIHAKS>2.0.ZU;2-7
Abstract
HNC is a major product of the dissociative recombination reaction of the im portant ionospheric ion HCNH+ although to date this neutral has not been id entified within Titan's atmosphere, nor considered as a component in ionosp heric or photochemical models, We have studied a simple pseudo-steady-state model for the formation and removal of HNC, in which the loss processes co nsidered are HNC protonation by reaction with H-bearing ions; reaction with H atoms, yielding HCN; reaction with CH3 radicals, to form CH3CN; and reac tion with a population of unidentified X radicals to yield further hypothes ized products. Using the ion abundances of C. N. Keller et al. (1998, Plane t. Space Sci. 46, 1157-1174) and of M. Banaszkiewicz et al. (2000, Icarus 1 47, 386-404), we find that the most important loss processes are the reacti ons with CH3 and with other unidentified radicals. According to our calcula tions, the HNC concentration reaches a peak of 10(4)-10(5) molecules per cu bic centimeter at an altitude of 1000-1100 km (i.e., close to the ionospher ic peak), but is very much reduced at lower altitudes. We find also that th e HNC/HCN ratio in Titan's atmosphere may approach unity at the ionization peak altitude and above. We discuss prospects for the detection of HNC, or its reaction products, during the Cassini mission. (C) 2001 Academic Press.