..._H

ACH2 was prepared by condensation of carbon vapor produced by an arc discharge between two carbon rods in a 10 mbar hydrogen atmosphere (Mennella et al. 2001). The label ACAR refers to hydrogen-free carbon grains produced by laser ablation of carbon electrodes in an argon atmosphere. In some cases, these grains were hydrogenated (ACAR_H) by exposure to hydrogen atoms produced by microwave-excited dissociation of molecular hydrogen (further details on the preparation of these grains can be found in Mennella et al. 2002). Some of these samples have been irradiated with 30 keV He⁺ ions (Baratta et al. 1996; Mennella et al. 2003).

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