Appearance Potentials by the Retarding Potentialhyphen;Difference Method for Secondary Ions Produced by Excitedmdash;Neutral, Excited Ionmdash;Neutral, and Ionmdash;Neutral Reactions

摘要

A timehyphen;ofhyphen;flight mass spectrometer with a retarding potentialhyphen;difference ion source has been used to measure appearance potentials and ionization efficiency curves for secondary ions. Reaction types studied include excited neutralhyphen;molecule, chargehyphen;transfer, attachment and branching ionhyphen;molecule reactions. The systems investigated were argon, krypton, methane, acetylene, 1ndash;3 butadiene, ethyl iodide, and methanemdash;krypton mixtures. Rarehyphen;gas molecular ions from excited neutralhyphen;molecule reactions were observed for Ar2+with appearance potentials at 14.94plusmn;0.02, 15.2plusmn;0.1, and 15.8plusmn;0.1 eV and for Kr2+at 13.20plusmn;0.02, 13.8plusmn;0.1, and 14.0plusmn;0.1 eV. A chargehyphen;transfer reaction for Krsngbnd;CH4produced CH3+at 14.6plusmn;0.1 eV corresponding to Kr+(2Pfrac12;). The activated complex formed by C4H6++C4H6from butadiene produces six different secondary ions. Ionization efficiency curves of the six secondary ions showed the same structure in the energy range to 2 eV above onset. Similar results were observed for two competitive reactions formed by C2H2++C2H2from acetylene, for energies below 14.5plusmn;0.2 eV. At higher energies, the ratio of secondary C4H3+/C4H2+changed by a factor of two thereby demonstrating the influence of reactions of excited C2H2*+. The predominant excitation level for the excited reaction was 17.0plusmn;0.2 eV. Ionization efficiency curves of the primary and secondary ions in the energy range near onset for all systems were essentially identical except for the collision complex C4H10I2+which was slightly different from that of the primary C2H5I+ion. The technique greatly improves the reliability of correlating primary ions with secondary ions and provides detail not otherwise measurable.