Trajectory and charge dependence ofLx-ray fluorescence followingAr++ Ar collisions

Abstract

The coincidence technique has been employed to determine the yield of L x-rays emitted following Ar/sup +/+Ar collisions of known incident energy T/sub 0/, scattering angle theta = 14/sup 0/, and scattered ion charge m. The range of T/sub 0/ studied, 50 to 575 keV, corresponds to a distance of closest internuclear separation r/sub 0/ from 0.18 to 0.03 A. As in the case of our earlier Auger-electron coincidence experiments on Ar/sup +/+Ar over this range, the present work uncovers evidence for two different L-vacancy-creating processes. The first process has a threshold at r/sub 0/ = 0.25 A and is the result of the transfer of two electrons out of the 4fsigma molecular orbital (MO). The second process, which appears when r/sub 0/ is made less than 0.13 A, is due to rotational transitions of up to six electrons from the 3d..pi.. and 3dsigma MO's into the 3ddelta MO. We find that there is a large increase in x-ray fluorescence associated with the 3d..pi.., 3dsigma..-->..3ddelta transition, an increase which is considerably in excess of that expected from available estimates. A qualitative explanation of this phenomenon is offered that takes into account combinations of long-lived autoionizing states involving outer-shell electrons, preferentialmore » pumping of L electrons up to the 3d radiative level, and finally, outer-shell-electron depopulation by prior Auger transitions. This interpretation is also consistent with the differing ion-charge x-ray-yield correlations that we find are characteristic of the 4fsigma and 3d..pi..,3dsigma processes.« less