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A model of comet comae. II - Effects of solar photodissociative ionization
Huebner, W. F.; Giguere, P. T.
AA(California, University, Los Alamos Scientific Laboratory, Los Alamos, N. Mex.), AB(California, University, Los Alamos Scientific Laboratory, Los Alamos, N. Mex.)
Astrophysical Journal, Part 1, vol. 238, June 1, 1980, p. 753-762. Research supported by the U.S. Department of Energy and NASA. (ApJ Homepage)
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NASA/STI Keywords:
Astronomical Models, Comet Heads, Gas Ionization, Molecular Gases, Photoionization, Photolysis, Abundance, Carbon Dioxide, Carbon Monoxide, Chemical Composition, Coma, Ion Production Rates, Kohoutek Comet, Photochemical Reactions, Positive Ions
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Improvements to a computer model of coma photochemistry are described. These include an expansion of the chemical reactions network and new rate constants that have been measured only recently. Photolytic reactions of additional molecules are incorporated, and photolytic branching ratios are treated in far greater detail than previously. A total of 25 photodissociative ionization (PDI) reactions are now considered (as compared to only 3 PDI reactions previously). Solar PDI of the mother molecule CO2 is shown to compete effectively with photoionization of CO in the production of observed CO(+). The CO(+) density peak predicted by the improved model, for CO2 or CO mother molecules, is deep in the inner coma, in better agreement with observation than the old CO2 model. However, neither CO2 nor CO mother molecule calculations reproduce the CO(+)/H2O(+) ratio observed in comet Kohoutek. PDI products of CO2, CO, CH4, and NH3 mother molecules fuel a complex chemistry scheme, producing inner coma abundances of CN, C2, and C3 much greater than previously calculated.

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