Cross Sections for Electron Capture into the Excited Leveln=6of Hydrogen by 5- to 70-keV Protons in Mg Vapor and in Neon

An optical technique has been used to investigate electron capture into the excited level $n=6\mathrm{}$ of hydrogen by 5- to 70-keV protons passing through magnesium vapor or neon. Photons from the Balmer ${\mathrm{H}}_{\delta }$ transition which are emitted downstream of the target were analyzed with a grating spectrometer and counted. From these the population of the level $n=6\mathrm{}$ and the cross section for electron capture into $n=6\mathrm{}$ have been obtained. Cross-section estimates for ionization of the level $n=6\mathrm{}$ collisions with Mg atoms are also presented. The electron-capture cross sections are consistent with $n^{-3\mathrm{}}$ extrapolations of electric-gap measurements for capture into higher quantum levels ($n\approx 9 \mathrm{to} 15$) reported by Il'in and co-workers, Futch and Moses, and Riviere. The results are compared with those of various theoretical models.