Scattering of very slow (3–10 eV) hydrocarbon ions CD 3+, CD 4[rad]+, and CD 5+ from room-temperature carbon (HOPG) surfaces

Abstract

Scattering of simple hydrocarbon ions CD 3 +, CD 4 +, and CD 5 + from room-temperature carbon (HOPG) surfaces was investigated at low incident energies of 3–10 eV. Mass spectra, angular and translational energy distributions of the product ions were determined. From these data, information on processes at surfaces, absolute ion survival probabilities, scattering diagrams, and effective mass of the surface involved in the collisions was determined. Incident ions CD 3 + and CD 5 + showed inelastic non-dissociative (CD 3 +) or non-dissociative and dissociative (CD 5 +) scattering, the radical cation CD 4 + exhibited both inelastic, dissociative, and reactive scattering, namely occurrence of H-atom transfer and C-chain build-up in reactions with hydrocarbons present on the room-temperature carbon surface. The absolute survival probability, at 10 eV and the incident angle of 30° (with respect to the surface), was about 12% for CD 5 +, and 0.3–0.4% for CD 3 + and CD 4 +. It decreased towards zero at lower incident energies. Estimation of the effective surface mass involved in the collisional process led to m(S) eff of about 29 a.m.u. for CD 3 + collisions, to 15–21 a.m.u. for inelastic and fragmenting collisions of CD 4 +, and 62 a.m.u. for CD 5 + collisions, corresponding roughly to the mass of one or several CH 3– (or C 2H 5–) terminal units of surface hydrocarbons. For the surface reaction of H-atom transfer in CD 4 + collisions, the effective mass m(S) eff was about 48 a.m.u. suggesting a more complicated surface process than a simple direct H-atom pick-up reaction.