EXPERIMENTAL AND MODEL ANGULAR-DISTRIBUTIONS OF ONE-ELECTRON AND 2-ELECTRON CAPTURE PROCESSES IN 0.5-20 EV U AR4+-AR COLLISIONS

We have measured and calculated state-resolved angular distributions of one- and two-electron-capture processes in 0.520 eV/u Ar4+-Ar collisions. The experimental energy-gain spectra show single-electron capture to six unresolved 4p LS terms, while no trace of a 4s population was found for laboratory collision energies below 200 eV. Semiclassical trajectory calculations, using a seven-channel Landau-Zener model for the probability flux on the multivalued deflection functions, show that the oscillations in the experimental 4p angular differential cross section are due to multiple rainbow scattering and that interference effects play a limited role. Experimental and calculated 4p angular distributions compare nicely over the whole energy range. For energies above 150 eV, true double-capture and transfer ionization with angular distributions consistent with a two-step electron-transfer process appear within the ±9°experimental acceptance. © 1990 The American Physical Society.