Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...271..662p&link_type=abstract
Astronomy and Astrophysics, Vol. 271, p. 662 (1993)
Astronomy and Astrophysics
Astrophysics
13
Atomic And Molecular Processes, Chemical Reactions, Interstellar Medium: Dust, Interstellar Medium: Molecules, Stars: Carbon
Scientific paper
Reactions of the ions D+, He+. , and Si +. with C60, and of the ions C+60, C2+ 620+., and C270+60, C+.70, and C2+70 with several neutrals of relevance to the chemistry of interstellar clouds and circumstellar envelopes recently have been studied with a selected-ion flow tube (SIFT) apparatus at 294±3 K in helium at pressures of 0.35-0.40 Torr. The implications of the results of these studies are discussed for the chemical evolution of interstellar clouds and circumstellar shells surrounding carbon-rich stars. Notable features of the ion-molecule reactivity of fullerenes include: the production of fullerene dications in the reaction of He+. with C60; the high selectivity of C+.60 and C+.70 towards radicals and amines; the predominance of association as a reaction channel of C+.60 with various neutral molecules; the tendency of fullerene dications to undergo association with unsaturated hydrocarbons; and the existence of activation energy barriers towards many charge-transfer and hydride abstraction reactions of fullerene dications, and proton transfer from functionalised fullerene dications. Other aspects of fullerene reactivity, not directly related to ion-molecule interactions, are also discussed. These include difficulties inherent in the dissociative recombination of fullerene ions and dications with electrons; the possible role of neutral and ionized fullerenes as a model for interstellar dust grain surface recombination of atomic hydrogen and other reactive species; production of fullerene dications by sequential cosmic-ray and UV photo-ionization and by cosmic-ray double ionization; and the possibility of fullerene cages acting as "traps" for cosmic rays within the interstellar medium. Possibilities for the interstellar detection of fulleranes, and fullerenes functionalised by amine and hydrocarbon moieties, are also discussed. It is argued that the fullerene cage structures, especially C60, should be very durable within the interstellar environment because of the lack of destruction mechanisms available for these species. In contrast, substituents attached to fullerene cages as a consequence of ion-molecule chemistry occurring within the interstellar medium are likely to be readily removed by UV irradiation within diffuse regions. For this reason, functionalised fullerenes (except for the slightly hydrogenated fulleranes) are not expected to be abundant in diffuse regions although they may be present in reasonable quantities within dense clouds.
Bohme Diethard K.
Javahery G.
Petrie Simon
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