Formation of Fast Excited H Atoms. I. Charge-Transfer Neutralization ofH+in He and Ar

A study has been made of the charge-transfer processes whereby neutral atoms of hydrogen are formed in the $3s$, $3p$, and $3d$ states as a result of the impact of protons on targets of helium and argon. Impact energies range from 75 to 400 keV. The experimental procedures involve the quantitative measurement of the Balmer-$\alpha$ radiation emitted by the spontaneous decay of atoms in these three states. The contributions of the three different states are separated by a time-of-flight technique that utilizes the different lifetimes of these states. The cross sections decrease rapidly with increasing energy and are greatest for the state of lowest angular-momentum quantum number. For a helium target, comparisons are made with a Born-approximation prediction; there is a marked discrepancy between theory and experiment for the $3p$ level but good agreement for the $3s$ and $3d$ levels.