Electron capture into the3sstate of atomic hydrogen byH+on Kr and Xe

Absolute cross sections for electron capture into the $3s$ state of atomic hydrogen have been measured for 10-150-keV proton impact on Kr and Xe. The experimental procedure involved the quantitative measurement of the Balmer-alpha radiation emitted by the spontaneous decay of fast hydrogen atoms in flight. The $3s$-state radiation was identified by its characteristic lifetime. The cross sections for both target gases reach a maximum in the projectile energy range under consideration. The Xe cross sections are approximately 40% higher than those for Kr near 25 keV but are similar above 80 keV. These values are consistent with existing $3s$ cross-section measurements and with an $n^{-3\mathrm{}}$ scaling of existing total electron-capture cross sections in accordance with Born-approximation predictions.