3d? excitation in slow Ne-Ar collisions

Abstract

The impact parameter dependence of Ar L-shell excitation in Ne-Ar collisions has been studied at collision energies of 200, 400 and 700 keV. Experimental vacancy production rates have been obtained by observing Ar-L Auger electrons in coincidence with scattered ions. A theoretical analysis of the experimental data has been performed by assuming vacancy production in the quasimolecular 3do. orbital to be the dominant mechanism for Ar L-shell excitation. Probabilities have been calculated separately for 3 do-excitation via 3 dO-3 dg-3 do-rotational coupling and via direct coupling to the continuum. The data at large impact parameters (where the calculated contribution from direct ionization is negligibly small) can be understood solely in terms of rotationaUy induced 3 do-excitation. The enhancement of the vacancy production rate over the rotational-coupling contribution observed for smaller impact parameters is explained qualitatively by the onset of direct 3dg ionization. Total cross sections for Ar-L vacancy production have been determined experimentally for collision energies ranging from 70 to 700 keV, and have been analyzed also in terms of 3 do. excitation.