Sequential Synchronous Mechanism for Double-Electron Capture: Insights into Unforeseen Large Cross Sections in Low-Energy Sn3++H2 Collisions

Remarkably large double electron capture cross sections, on the scale of 10−15  cm2, are observed in low-energy (<50  eV/u) collisions between Sn3+ and H2. Given that the reaction is energetically highly unfavorable, one would expect negligibly small cross sections. Through the propagation of vibrational wave packets on coupled multiple potential energy surfaces, a novel charge transfer mechanism, driven in tandem by ion motion and molecular vibration, is revealed, offering insights into the unusual energy dependence of the measured cross sections.