Some similarities and differences in collisional electron loss ofH−,H2+, andHe+

We have measured the electron-loss peak as a function of angle for the following collisions at 0.5 MeV/amu: ${\mathrm{H}}_2^{+}$-Ar, ${\mathrm{H}}_2^{+}$-Ne, ${\mathrm{H}}_2^{+}$-Kr, ${\mathrm{He}}^{+}$-Kr, and ${\mathrm{H}}^{-}$-Kr. Electron energy spectra at an angle of 6° and complete angular distributions are shown for the last three systems listed above. The energy at which the electron-loss peak has its maximum and the width at half-maximum of the peak are compared for all five systems in the angular range $1.5\le \theta \le 10°$. Our results suggest that, as previously indicated, the angular distribution of the electron-loss peak seems to be determined by the target. When the projectile is a positive ion the energy of the electron-loss peak seems to be independent of target or projectile and therefore is a general feature of the process. The width of the electron-loss peak and its dependence on angle seems to depend primarily on the projectile. Electron-scattering-model calculations do no predict features of the electron-loss peaks which are angular dependent.