Determination of complex ionization amplitudes by (e,2e) spectroscopy

[ital (]e,2[ital e]) spectroscopy has been used to investigate interference between resonant dipole and nonresonant monopole electron-impact ionization of Cd. A technique is described which allows the experimental determination of the relative magnitude and phase of the amplitudes for these processes. The method makes use of the rapid variation with energy of the continuum phase in the region of autoionizing resonances. The experimental relative dipole/monopole amplitude for momentum transfer 0.18 a.u. is found to be in substantial disagreement with a plane-wave Born approximation calculation.