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Astron. Astrophys. 325, 1264-1279 (1997)

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Chemical reactions in protoplanetary accretion disks

II. Carbon dust oxidation

F. Finocchi 1, H.-P. Gail 1 and W. J. Duschl 1, 2

1 Institut für Theoretische Astrophysik, Universität Heidelberg, Tiergartenstraße 15, D-69121 Heidelberg, Germany
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Received 6 November 1996 / Accepted 27 January 1997

Abstract

This paper considers the gas phase chemistry in a protoplanetary accretion disk, especially the chemistry initiated in the gas phase by destruction of dust close to the central star.

Slow radial particle transport moves gas and dust from the cold outer parts of a protoplanetary accretion disk into its warm central part where chemical reactions in the gas phase are activated. At the same time gases frozen on the surface of dust grains are vaporized and later the dust grains themselves are vaporized or destroyed by chemical surface reactions. In this paper we take into account oxidation processes of carbon dust by OH molecules and free O atoms. Oxidation by OH molecules turns out to be very efficient and strongly modify the hydrocarbon chemistry in the protoplanetary disk. Due to the slow conversion of hydrocarbons to CO at low temperatures we find that large amounts of methane and more complex organic molecules are formed in the region between the present positions of Venus and Mars. Closer to the protosun, these are converted into CO.

Key words: accretion disks – molecular processes – solar system: formation

Send offprint requests to: H.-P. Gail, (gail@phyllis.ita.uni-heidelberg.de)

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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