The three-body Coulomb problem has been explored in kinematically complete experiments on single ionization of helium by $100\mathrm{MeV}/\mathrm{u}{\mathrm{C}}^{6+}$ and $3.6\mathrm{MeV}/\mathrm{u}{\mathrm{Au}}^{53+}$ impact. Low-energy electron emission ( $E_e<150\mathrm{}\mathrm{eV}$) as a function of the projectile deflection ${\vartheta }_p$ (momentum transfer), i.e., the Bethe surface [[15]], has been mapped with $\Delta {\vartheta }_p\pm 25$ nanoradian resolution at extremely large perturbations ( $3.6\mathrm{MeV}/\mathrm{u}{\mathrm{Au}}^{53+}$) where single ionization occurs at impact parameters of typically 10 times the He $K$-shell radius. The experimental data are not in agreement with state-of-the-art continuum distorted wave–eikonal initial state theory.

• Received 25 May 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.223201