Survey of chemi-ionization reactions in accelerated atom–O2 crossed-molecular beams

Abstract

The chemi‐ionization reactions, associative ionization, and rearrangement (reactive) ionization, and the electron transfer reaction have been investigated in the crossed‐molecular beam collisions of more than 20 accelerated (by sputtering) metal and nonmetal atoms with O₂ molecules. The observations support a generalization on the scope of these chemi‐ionization reactions and their relation to electronic structure, namely that associative and rearrangement ionization reactions do not occur for collision partners for which the thermodynamic threshold energy for electron transfer is lower than the thresholds for the chemi‐ionizations. On the other hand, rearrangement and associative ionization may be prominent reaction channels when their thermodynamic thresholds are less than that for electron transfer. Relative cross sections for Ce⁺, CeO⁺, and CeO₂⁺ formation for collision energies of Ce+O₂ up to 50 eV (cm) are presented. A substantial threshold for associative ionization is observed for this system.