Steep dependence of recoil-ion energy on coincident projectile and target ionization in swift ion-atom collisions

The first measurements of the mean energies ${E}_{r}$ of highly charged recoil ions detected in coincidence with multiply ionized swift projectiles are reported. Beams of 23-, 27.6-, and 33-MeV ${\mathrm{Cl}}^{5+}$ produced Ar recoil ions whose mean energies exhibited a strong dependence on the product (qr) of final projectile and recoil charge states. For large qr values, ${E}_{r}$ is substantially larger than earlier estimates, and allows inference of characteristic impact parameters without requiring measurements of projectile scattering angle.