Electron Capture into the Metastable2sState in Collisions of Protons with Hydrogen Atoms

Abstract

The cross section ${\sigma }_{2s}\left(\mathrm{H}\right)$ for the atomic collision reaction ${\mathrm{H}}^{+}+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}\to \mathrm{H}\mathrm{}\left(2s\right)+{\mathrm{H}}^{+}$ has been measured for proton energies between 3 and 23 keV. The data provide a relatively sensitive test of available cross-section calculations. Good agreement exists with a three-state atomic-eigenfunction expansion calculation that includes as an intermediate state only the $2s$ state about the target proton. The Born approximation fails to predict the measured energy dependence below 20 keV.