Associative Detachment of H$^{-$ + H $\rightarrow$ H$_{2}$ + e$^{-}$

TL;DR

This study measures and analyzes the associative detachment reaction of hydrogen anions with hydrogen atoms across a range of collision energies, confirming that the reaction rate diminishes significantly above 2 eV, supported by updated theoretical models.

Contribution

The paper provides new experimental data extending previous measurements up to 4.83 eV and refines theoretical models to better understand the reaction dynamics of H$^-$ with H.

Findings

Reaction rate drops off above 2 eV collision energy

Experimental data aligns with updated theoretical calculations

Resonance effects influence reaction outcomes at higher energies

Abstract

Using a merged beams apparatus we have measured the associative detachment (AD) reaction of ${\rm H}^- + {\rm H} \to {\rm H}_2 + e^-$ for relative collision energies up to \textit{E}$_{\rm{r}} \leq 4.83$ eV. These data extend above the 1 eV limit of our earlier results. We have also updated our previous theoretical work to account for AD via the repulsive $^2\Sigma^+_{\rm g}$ H$_2^-$ potential energy surface and for the effects at $E_{\rm r} \ge 0.76$ eV on the experimental results due to the formation of H$_2$ resonances lying above the ${\rm H} + {\rm H}$ separated atoms limit. Merging both experimental data sets, our results are in good agreement with our new theoretical calculations and confirm the prediction that this reaction essentially turns off for $E_{\rm r} \gtrsim 2$ eV. Similar behavior has been predicted for the formation of protonium from collisions of antiprotons and hydrogen atoms.