State-selective capture in collisions between ions and ground- and excited-state alkali-metal atoms

Total cross sections for state-selective electron capture in collisions between ions and alkali-metal atoms have been calculated by means of a three-body classical-trajectory Monte Carlo (CTMC) method using model potentials to describe the electron–ionic-core interactions. Calculations have been performed for ${\mathrm{Na}}^{+}$-Na(28d) collisions and for ${\mathrm{N}}^{5+}$ and ${\mathrm{Ar}}^{8+}$-Cs(6s) collisions. The collision velocity range corresponds to 0.5≲${\mathit{v}}_{\mathit{p}}$/${\mathit{v}}_{\mathit{e}}$≲2, where ${\mathit{v}}_{\mathit{p}}$ is the projectile velocity in the laboratory frame and ${\mathit{v}}_{\mathit{e}}$ is the initial orbital velocity of the electron bound to the alkali-metal core. In the case of ${\mathrm{Na}}^{+}$+Na(28d) collisions, calculations of the final n,l,m distributions show the importance of the electron-capture cross sections into states with m>1. For the case of multiply charged ion–Cs(6s) collisions, a predominance of electron capture to nearly circular states (large l values) is predicted for cross sections near the maximum of the n distribution. When the ${\mathit{e}}^{\mathrm{-}}$-${\mathrm{Cs}}^{+}$ interaction is described by a realistic model potential, the CTMC calculations are found to be in good agreement with recent measurements of the final n values that are predominantly populated after single-electron capture.