Cross Section for Metastable Production in Low-EnergyHe+-He Collisions

Abstract

Metastable He atoms produced by charge exchange of slow ${\mathrm{He}}^{+}$ with He were detected by secondary electron emission from a tungsten target. The cross section for metastable production rose from a threshold near 22 eV to a peak value of 2.2×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$ ±50% at 27 eV and decreased to a minimum at 32 eV (center-of-mass energy). A subsequent rise was measured up to 110 eV and was attributed to the increased production of ${\mathrm{He}}^m$ and, to a smaller extent, to kinetic emission of secondary electrons at the higher energies.