Absolute Excitation Cross Sections ofHe+in 20-100-keVHe+-He Collisions Using Energy-Loss Spectrometry

Application of positive-ion energy-loss spectrometry has been extended to include experimental determination of absolute excitation cross sections of ground-state helium ions. Helium ion-atom collisions were studied for impact energies ranging between 20-100 keV, in 10-keV intervals. The data were taken with an apparatus resolution between 0.6-0.8 eV full width at half-maximum (FWHM). Cross sections for transitions from ground state to the second and third principal quantum levels of the ion plotted as a function of impact energy were still rapidly increasing at 100 keV. The cross sections at this energy were (1.64 ± 0.28) × ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$ for ${\mathrm{He}}^{+}\left(1\mathrm{}{}_{}{}^2{}_{}{}^{}s_{\frac{1}{2}}^{}{}_{}{}^{}\right)\to {\mathrm{He}}^{+}\mathrm{}(n=2\mathrm{})\mathrm{}$ and (3.46 ± 0.45) × ${10}^{-19\mathrm{}}$ ${\mathrm{cm}}^2$ for ${\mathrm{He}}^{+}\left(1\mathrm{}{}_{}{}^2{}_{}{}^{}s_{\frac{1}{2}}^{}{}_{}{}^{}\right)\to {\mathrm{He}}^{+}\mathrm{}(n=3\mathrm{})\mathrm{}$.