| Popis: |
Total cross sections for electron capture have been measured for ${\mathrm{O}}^{q+}(1\ensuremath{\le}q\ensuremath{\le}8)$, ${\mathrm{Fe}}^{q+}(4\ensuremath{\le}q\ensuremath{\le}15)$, ${\mathrm{Mo}}^{q+}(4\ensuremath{\le}q\ensuremath{\le}18)$, ${\mathrm{Ta}}^{q+}(3\ensuremath{\le}q\ensuremath{\le}19)$, ${\mathrm{W}}^{q+}(6\ensuremath{\le}q\ensuremath{\le}15)$, and ${\mathrm{Au}}^{q+}(5\ensuremath{\le}q\ensuremath{\le}16)$ incident on H and ${\mathrm{H}}_{2}$ in the velocity range 2.2-6.2\ifmmode\times\else\texttimes\fi{}${10}^{8}$ cm/s. Both the scaling of the capture cross sections with projectile charge and their velocity dependence are investigated and compared to current theoretical models. In the range of charge states and velocities investigated, the cross sections, in general, are observed to decrease uniformly with increasing projectile velocity and to increase monotonically with increasing projectile charge. The charge dependence of the cross sections becomes stronger with increasing projectile velocity. In the present range of velocities, the ratios of the cross sections measured on ${\mathrm{H}}_{2}$ and H targets decrease with increasing projectile charge, while increasing as a function of velocity. For the lighter projectiles Fe and Mo, localized deviations from the expected smooth increase of the capture cross sections with increasing projectile charge at constant velocity were observed in the vicinity of projectile charge states corresponding to closed-shell configurations. These observed "dips" are strongly correlated with variations in calculated ionic projectile radii. For the heavier projectiles Ta, W, and Au, oscillations superimposed on the expected monotonically increasing $q$ dependence were observed, having amplitude and phase that are only weakly dependent on projectile species. This oscillatory behavior is attributed to interference between the long-range Coulomb and short-range (screened) Coulomb interactions characterizing the collision. |
