Unraveling Electron Transfer in the Oxidation of Yttrium Metal Atoms: Dual Pathways from Reactive and Nonreactive Imaging

The intricate mechanisms underlying electron transfer and structural evolution are essential to understanding the oxidation dynamics of transition metal atoms; however, accurately measuring the mechanisms remains challenging. In this study, utilizing laser ablation-crossed beam and time-sliced ion velocity imaging techniques, we identified two distinct electron transfer mechanisms in the reactions of Y and O₂ based on reactive and nonreactive scattering measurements across varying collision energies. (1) Low-barrier end-on pathway: Electron transfer occurs through a collinear Y-O-O geometry with a low activation barrier, evidenced by rebound scattering of YO products at low collision energy and backward scattering of Y reactants at higher energies. (2) High-barrier side-on pathway: Electron transfer proceeds through a side-on geometry, presenting a higher activation barrier that facilitates the formation of long-lived O-Y-O intermediates, which is characterized by the backward-forward peaking angular distribution of YO products and broad energy distributions of O₂ reactants at high collision energy.