Electron capture by slowAlq+ions colliding with hydrogen

Total electron-capture cross sections have been measured for collisions of ${\mathrm{Al}}^{\mathrm{q}+}$ (q=2–10) with H and ${\mathrm{H}}_2$ in the 20–120-eV/amu energy range. The general trend of the cross sections for both H and ${\mathrm{H}}_2$ is an approximately linear increase with ionic charge state. The ${\mathrm{Al}}^{2+}$+H and ${\mathrm{Al}}^{3+}$+H systems were investigated theoretically using the molecular-orbital method with a pseudopotential to represent the ${\mathrm{Al}}^{3+}$ ion core. Coupled-channel calculations realize good agreement with experiment. An anomalously small cross section for ${\mathrm{Al}}^{2+}$+H is attributed to the fact that of the ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }$ and ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }$ entrance channels, only the ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }$ molecular state contributes to the cross section.