Lyman-Alpha Production inH+−H(1s)Collisions

Abstract

Lyman-alpha production in collisions between protons and hydrogen atoms has been measured in a crossed beam experiment, within the energy range 600 eV to 30 keV. The Lyman-alpha photons result both from excitation of thermal target atoms —${\mathrm{H}}^{+}+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}\to {\mathrm{H}}^{+}+\mathrm{H}\mathrm{}\left(2p\right)\mathrm{}$— and from electron capture into excited states of the projectiles —${\mathrm{H}}^{+}+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}\to \mathrm{H}\mathrm{}\left(2p\right)+{\mathrm{H}}^{+}$. These two processes are experimentally distinguishable in terms of the Doppler shift in the capture radiation. Measurements of the angular distribution of the Lyman-alpha photons, made with an oxygen-filtered iodine-filled counter, enable the signals from the two processes to be separately determined. Relative cross sections so obtained are normalized with the aid of earlier measurements of Lyman-alpha production in $e^{-}-\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$ collisions. The results are discussed in the light of recent theoretical developments.