Intra-atomic Electron-Electron Scattering in p-He Collisions (Thomas Process) Investigated by Cold Target Recoil Ion Momentum Spectroscopy

We have performed a kinematically complete experiment for the transfer ionization reaction 0.15{endash}1.4 MeV p+He{r_arrow}H{sup 0}+He{sup 2+} +e{sup {minus}} by measuring the three-dimensional momentum vector of the He{sup 2+} ion in coincidence with the scattering angle and the plane of the H{sup 0} . In the measured fourfold differential cross section we can clearly distinguish between the independent two-step process of capture plus ionization and the correlated e -e Thomas scattering. We find a v{sup {minus}7.4{plus_minus}1}{sub P} scaling for the total cross section of the e -e Thomas process. {copyright} {ital 1997} {ital The American Physical Society}