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The electron transfer mechanism was investigated for the single-electron-capture process in 3-keV/u ArAr8+ -He collisions with cold target recoil ion momentum spectroscopy. The different state-selective electron capture processes were identified for one 1 s electron of He capture into 4 s, 4 p, 4 d - 4 f, and 5 s - 5 p states of ArAr8+. We observed that 1 s to 4 s capture mainly happens at small transverse recoil ion momentum, while 1 s to 4 p capture mainly happens at large transverse recoil ion momentum. By comparing the measured projectile scattering angle distributions to the theoretical calculations, it is suggested that 1 s to 4 s and 1 s to 4 p state-selective capture processes are mainly caused by radial and rotational coupling effects, respectively, and the 4 p ± 1 quantum states are preferred. [ABSTRACT FROM AUTHOR]

Autoionization decay from doubly excited states of Ne6+[1s²3lnl (n=3,4,5)] (symmetric configurations) as well as the Coster-Kronig transition from doubly excited states of Ne6+[1s²2pnl(n?7)] (asymmetric configurations) are observed in the transfer ionization reaction channel of 80 keV/u Ne8+-He collisions. It has been predicted that the formation of symmetric configurations results from uncorrelated double-electron capture processes [Z. Chen and C. D. Lin, Phys. Rev. A 48, 1298 (1993)], and the formation of asymmetric configurations probably results from correlated double-electron capture caused by the dynamical electron-correlation effects which are attributed to small internuclear distances. However, previous experimental measurements were not able to obtain information about the dependence on internuclear distance which can be reflected in the transversal recoil-ion momentum. In this work, we measure the recoil-ion momentum in coincidence with the ejected electron velocity and find that the observed transverse recoil-ion momentum is smaller for the formation of symmetric Ne6+[1s²3lnl(n=3,4,5)] states than the formation of asymmetric Ne6+[1s²2pnl(n?7)] states. Since large momentum transfer occurs for small internuclear distances (strong electron-electron interactions) and small momentum transfer occurs for large internuclear distances (weak electron-electron interactions), the results indicate that dynamical electron correlation is important for the formation of the asymmetric states. [ABSTRACT FROM AUTHOR]

We measured the kinetic energy distributions of the fragment ions of doubly and quadruply ionized argon dimers using 3000 eV electron impact. For the dissociation of (Ar2)2+, the peak that indicates radiative charge transfer is observed, where the outer-shell ionization (dominant in highly charged ion collision) and the inner-shell ionization (preferential in x-ray experiments) have approximately equal contributions. For the dissociation of (Ar2)4+, the interatomic Coulombic decay and electron-transfer-mediated decay are first observed in the electron-impact process. [ABSTRACT FROM AUTHOR]