Electron transfer in keV-energyHe++4collisions. III. Experimental tests of the close-coupling calculations forHe++4-H(1s)collisions

Two experimental tests of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$-$\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$ close-coupling collision calculations were performed with a highly mass-resolved ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$ incident ion beam and an atomic hydrogen scattering target. The total single-electron-transfer cross section ${\sigma }_{21}\left(\mathrm{H}\right)$ was measured for ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$ energies between 7 and 144 keV, with the results in better agreement with molecular-state calculations than with theory employing atomic states. Above 25 keV this cross section is 50% above values obtained by Shah and Gilbody for incident ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$ with the same collision velocity. Also measured was the cross section ${\sigma }_{21}^{*}\left(\mathrm{H}\right)$ for single-electron transfer into the $2s$ state of ${\mathrm{He}}^{+}$ using an ion-photon time-coincidence technique over the ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$ energy range 7 to 70 keV. These data differ with the corresponding ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$-$\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$ data of Shah and Gilbody at the higher energies. For ${\sigma }_{21}^{*}\left(\mathrm{H}\right)$, the observed energy dependence as well as the magnitude at the lower energies are in marked disagreement with all close-coupling results.