Nonequilibrium chemical analysis of the coma of comet P/Stephan-Oterma

A computer code to calculate the time-dependent nonequilibrium chemistry taking place within the coma of a comet has been developed. This code incorporates 1249 chemical reactions involving 128 species. Models were fit to data on Comet P/Stephan-Oterma (A. L. Cochran and E. S. Barker, 1985, Icarus62, 72–81). It was shown that (1) HCN is the parent for CN; (2) C₂H₂ is a parent for C₂; (3) pure gas-phase chemistry with known species cannot adequately reproduce the observed C₃ but a single step process can; and (4) at least prior to perihelion, the vaporization rate seems to have been controlled by water vaporization.