Evidence for target outer-shell excitation mediated by electron correlation in single-electron-capture collisions of slow He2+ ions with Ar atoms

Z Y Song,K L Han,X C Wang,D Fischer,Z W Li

doi:10.1103/physreva.102.042820

Abstract

We have performed kinematically complete experiments on single-electron capture in slow ${\mathrm{He}}^{2+}$-Ar collisions. Besides the pure capture to the ${\mathrm{He}}^{+}(n=2)$ level, capture into the deep ${\mathrm{He}}^{+}(n=1)$ state with simultaneous excitation of another target electron is also observed. In contrast to the pure capture, the total cross section for this two-electron transition decreases with increasing collision energy, and its angular-differential cross section exhibits a much slighter slope. We take these observations as evidence for electron capture mediated by electron-electron interactions.

Highlights

The process of correlated two-electron transition generally exists in the field of atomic physics
We show evidence for target excitation mediated by the e-e interaction in single-electron capture collisions of He2+ ions with Ar atoms
As discussed in Refs. [22,23,24], the stronger peak on the right corresponds to the PSEC reaction, i.e., a valence electron of the Ar atom is captured to the n = 2 orbital of the He+ ion, He2+ + Ar → He+(n = 2) + Ar+(3p5)

Summary

INTRODUCTION

The process of correlated two-electron transition generally exists in the field of atomic physics. By increasing the collision energy to 240–2500 keV, SchOoffler and co-workers further investigated the TTE reaction for this collision system [8] and found a peak structure around θP ≈ 0.5 mrad for the ratio of TTE and PSEC They attributed it to the further momentum exchange between the projectile and another target electron in the second interaction of an independent two-step process. By extending the molecular classical overbarrier model [11], Cederquist [12] explained the experiments with a three-step mechanism, in which the loosely bound one of the two consecutively captured electrons is recaptured at a critical internuclear distance by the target to its excited state (TTE) because of the interaction of the double-capture quasimolecular channel and the TTE channel Target excitation through this re-capture mechanism was observed following multiple-electron capture in collisions of 15N7+ ions with Ar atoms [13].

EXPERIMENTAL APPARATUS

RESULTS AND DISCUSSION

CONCLUSIONS