Cross Sections for the Production of Lyman-$\alpha$ Radiation by Fast-Proton Impact on ${\mathrm{H}}_2$

Absolute cross sections have been measured for the production of Lyman-$\alpha$ radiation by proton impact on ${\mathrm{H}}_2$ in the energy range from 20 to 120 keV. Radiation from slow H atoms produced by dissociative excitation of the ${\mathrm{H}}_2$ molecule was separated from the radiation from fast hydrogen atoms produced by electron capture by using a Doppler-shift technique. Reasonable agreement is obtained with other investigators where the cross sections overlap. The fast-atom emission exhibits a sharp monotonic decrease with energy, characteristic of charge transfer. The slow-atom emission also monotonically decreases with energy but not nearly as rapidly. It is estimated that about 4% of the total charge transfer goes into producting fast atoms in the $2p$ state.