Hot atom chemistry ¡Recoil carbon/Carbon-11 ("C)/ Atomic carbon • water vapour system /FormaldehydeSummary The chemical reactions of recoil "C with H 2 0 vapour (28 mbar) were studied at ambient temperature in the pure system and after addition of 1 bar neon moderator. Atomic carbon was generated in situ via the 1 Όίρ,αρη) 11 C-reaction and via recoil-implantation from a thin BN-layer after the 14 N (ρ, a)" C process. The chemical consequences were followed over a radiation dose range from 5 · 10" 2 to 34 eV per target molecule. Typical products were "CO, "CH 4 and "C0 2 . The yield of "CO was found to be 98 % at the lowest dose. With increasing dose, the yield of 11 CO decreased, giving rise to the secondary radiolytic products 11 CO 2 and 1 'CH,,. It is assumed that a primarily formed carbonwater complex decomposes into 11 CO and Η,. Formaldehyde was not formed.