Electron Capture into the3sState of Hydrogen by Fast-Proton Impact on Gases

Absolute cross sections for electron capture into the $3s$ state of hydrogen by fast-proton (5-115 keV) impact have been determined for impact on He, Ar, Ne, ${\mathrm{N}}_2$, ${\mathrm{H}}_2$, and ${\mathrm{O}}_2$. The helium cross sections agree with Mapleton's Born-approximation calculations at about 115 keV. Curves of argon and neon cross sections versus proton energy show structure similar to that found in the $2s$ state by Jaecks et al., indicating that the influence of ground-state capture extends to the $n=3\mathrm{}$ level. The ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ cross sections are similar. The ${\mathrm{O}}_2$ curve shows additional structure. At 100 keV the ratio of the $3s$ capture to the total capture is 0.03 to within 15% for all six gases.