Double Ionization of Helium and Neon for Fast Heavy-Ion Impact: Correlated Motion of Electrons from Bound to Continuum States

Double ionization of He and Ne by charged particle impact was explored in kinematically complete experiments measuring the final momenta of the two emerging electrons $({\mathbf{P}}_{e1\mathrm{}}^f,{\mathbf{P}}_{e2\mathrm{}}^f)$ and of the recoiling target ion ${\mathbf{P}}_R^f$. The momentum transfer from the $3.6\mathrm{MeV}/u$ ${\mathrm{Se}}^{28+}$ projectile to the electrons is found to be negligibly small. Thus distinct patterns observed in the ${\mathbf{P}}_{e1\mathrm{}}^f$-versus- ${\mathbf{P}}_{e2\mathrm{}}^f$ spectra sensitively reflect the details of the electrons' correlated motion. Classical calculations reasonably describe the data only when the $(e-e)$ interaction during the ionization reaction is included.