Formation of Metastable Hydrogen Atoms by Charge Transfer

Measurements are presented of the total cross sections for formation of metastable hydrogen atoms by charge transfer as protons traverse targets of helium, argon, nitrogen, and oxygen. Projectile energies range from 4 to 26 keV. An ${\mathrm{H}}^{+}$ projectile beam was directed into a cell containing the target gas and emerged into an evacuated region where the metastable-state content was determined. The $\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$ flux was monitored by electric field mixing of this state with the $2p$ level and detection of the resulting Lyman-$\alpha$ photon. The relative variation of cross section with projectile energy for targets of He and Ar is in agreement with previous work. For oxygen the cross section increases with energy from 4 to 10 keV and remains constant from 10 to 26 keV; for nitrogen the cross section increases monotonically with increasing energy.