Electron capture into the4sstate of atomic hydrogen byH+impact on noble gases

Cross sections for electron capture into the $4s$ state of hydrogen have been measured for 10 to 150-keV protons incident upon He, Ne, Ar, Kr, and Xe. The cross-section curves for each gas reach an apparent maximum in this projectile-energy range. The values for Kr and Xe are consistent with an $n^{-3\mathrm{}}$ scaling of previous $3s$ capture-cross-section measurements in this projectile range. The He, Ne, and Ar values are in excellent agreement with previously reported measurements above 60 keV but give consistently higher values than those measurements at the lower energies. There are no comparable Kr and Xe values in the literature. The shape and magnitude of the excitation functions for these gases indicate that the internal structure of the target atom is an important factor in the charge-transfer process.