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J. Helbert, H. Rauer (DLR), D. Boice, W. Huebner (SwRI)
We will present the recent progress on our work on the evaluation of the chemistry of the C2 and C3 radicals in the coma of comet C/1995 O1 Hale-Bopp. The chemistry of the C-bearing molecules in the cometary coma is still not fully understood. A number of parent molecules have been proposed for C2. Only recently two of them, C2H2 and C2H6, could be detected in the extremely bright comets Hale-Bopp and Hyakutake. C3H4 has been proposed as the parent molecule for C3, but until now, there has been no detection of C3H4, or any of its daughter-molecules except C3, in a cometary coma.
We are using observations of C2 and C3 emissions obtained during a long-term monitoring program of comet Hale-Bopp (Rauer et al., Science, 1997, 275; ACM, 1999). Due to the high activity of this comet it was possible to detect C3 emissions in the coma as far as 7 AU from the sun and C2 emissions up to 5 AU. This exceptional dataset allows to analyze possible reaction pathways for the formation of the C2 and C3 radicals. For this study we investigate the various reaction pathways by using a restricted chemistry code including only photochemistry and a detailed neutral coma model including in addition a detailed gas-phase chemistry, dust entrainment by the gas and seperate flow of the neutral gas.
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