The angular correlation for ($e,2e$) experiments involving knock out of the least-bound electrons in helium and argon is compared with theory. A distorted-wave off-shell impulse approximation is derived and shown to fit the data within experimental error. Outstanding features are that the shape of the angular correlation at energies from 200 to 800 eV depends only on the momentum transfer. Hence the angular correlation is directly related to the momentum wave function of the struck electron. The reaction is sensitive enough to distinguish between different approximations for the wave function.

• Received 14 May 1973

DOI:https://doi.org/10.1103/PhysRevA.8.2494