A Novel Merged-Beams Apparatus for Studying Anion-Neutral Reactions*

We are developing a novel apparatus at the Columbia Astrophysics Laboratory to study anion-neutral reactions. Beginning with an anion beam, we use photodetachment to generate a self-merged, anion-neutral beams arrangement. Laboratory beam energies are in the keV range. Because the beams run co-linear, center-of-mass energies from the meV to keV range will be achievable. Our proof-of-principle measurement is the associative detachment (AD) reaction ${\rm H}^- + {\rm H} \to {\rm H}_2 + {\rm e}^-$. Published values for this process differ by over a factor of 5. Measurements using our novel apparatus will help to resolve this fundamental issue in physics and chemistry. We will observe the AD reaction by detecting fast H$_2^+$ ions formed through ionizing collisions of the AD-generated H$_2$ with the background gas in the vacuum chamber. Here we present the current status of the project and discuss our future plans.