Z, Velocity, and Charge Dependence of Zero-Degree Electron "Cusps" from Charge Transfer to Continuum States of Bare and Highly Ionized Projectiles

Data on continuum electron capture and loss for bare and highly ionized ${\mathrm{C}}^{q+}$, ${\mathrm{O}}^{q+}$ ions traversing Ar at energies 1.6-2.8 MeV/A reveal striking disagreements with corresponding theories. We demonstrate a velocity-independent ($\sim Z^{2.2\pm 0.2}$) scaling for continuum capture by bare ions, a $Z$-independent velocity scaling, and an approximately $q$-independent ($q=6, 7, 8$) equality of continuum electron-capture and-loss cross sections at velocities corresponding to ∼2 MeV/A.