Strongly enhanced backward emission of electrons in transfer and ionization

We studied three-dimensional angular distributions and longitudinal momentum spectra of electrons ejected in transfer plus ionization (TI), i.e., the ejection of one and the capture of a second target electron, for ion-helium collisions. We observe a pronounced structure strongly focused opposite to the projectile beam direction, which we associate with a new correlated TI mechanism proposed recently. This process contributes significantly to the total cross sections over a broad range of perturbations η, even at η as large as 0.5, where uncorrelated TI mechanisms were thought to be dominant. © 2012 American Physical Society.