Measurements of the Associative Detachment Reaction H- + H → H2 + e- for Modeling Protogalaxy and First Star Formation in the Early Universe
Abstract
Molecular hydrogen plays a central role in the cooling and formation of protogalaxies and first stars in the early universe. The dominant H2 formation mechanism during this epoch is the associative detachment (AD) reaction H- + H → H2 + e-. Previously published values for this process differ by almost an order of magnitude. These uncertainties hinder our ability to reliably model this epoch of the universe, limiting our ability to understand the formation of protogalaxies, the characteristic masses of the first stars, and the cooling times for formation of the first stars. We have developed a novel merged-beams apparatus to measure, for the first time, the energy resolved cross section for this reaction. Beginning with an H- beam, we use an infrared laser to convert ∼ 10% of the beam into ground state H via photodetachment. This generates a self-merged, anion-neutral beams arrangement. Laboratory energies are in the keV range; but because the beams co-propagate, center-of-mass energies from the meV to keV range are achievable. We have measured the cross section for energies from 3.7 meV to 4.8 eV. Our results confirm recent non-local calculations but are not in agreement with other previously published theoretical results or with published flowing afterglow measurements. This work was supported in part by the NSF Divisions of Chemistry and Astronomical Sciences.
- Publication:
-
American Astronomical Society Meeting Abstracts #220
- Pub Date:
- May 2012
- Bibcode:
- 2012AAS...22020906S