Capture dissociation of H2+ in rare gases and small hydrocarbons

Translational energy spectroscopy of H+ and H− ions, produced by the two-collision capture-dissociation of 6 keV H2+ with rare gas (He, Ne, Ar, Kr) and small hydrocarbon [CH4, C2H6, C3H8, C2H4, C3H6, C4H8 (but-2-ene)] targets, is performed. The first collision involves single-electron capture by H2+ into some stable or metastable state H2*; the efficiency of this process is strongly dependent on the number of available target gas valence electrons. Proof of the formation of electronically excited H2* is presented. The second collision step involves dissociation of H2* to H+ and/or H− via either dissociative re-ionisation, dissociative capture, or ion pair formation. Measured translational energy release distributions and relative cross-sections for ionic fragment formation are consistent with the proposed capture-dissociation mechanisms