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E. A.-N. Deneault, D. D. Clayton (Department of Physics and Astronomy, Clemson University)
In the expanding and cooling supernova interior, carbon and oxygen chemical reactions establish a steady-state abundance of linear carbon chains. For an increase in chain length of two C atoms, the abundance declines by a factor near 10-3. At sufficient length, it becomes energetically preferable for the linear chain to isomerize into a monocyclic ring isomer. These rings, which are more resistant to oxidation than linear chains, form the nucleation sites for the growth of large carbon grains which are found in meterorites. However, the rate of isomerization, and the critical length at which spontaneous isomerization occurs rapidly enough is presently unknown. To produce the observed abundances of large supernova graphite grains, each gram of C atoms must form about 1000 carbon rings during the first two years of expansion after the explosion. How the critical rate of isomerization affects the final abundances of large carbon grains is discussed.
Research supported by NASA Cosmochemistry Program