A second-order continuum distorted-wave theory of charge transfer at high energy

Abstract

The differential cross section (DCS) for electron capture at asymptotically high, but non-relativistic, energy is investigated within the second-order distorted-wave approximation given by second-order continuum distorted waves (CDW2) and is compared with second-order Oppenheimer-Brinkmann-Kramers plane waves (OBK2). It is concluded that the inclusion of explicit intermediate states in both theories ensures a uniquely determined value for the high energy 1s-1s DCS at the forward peak and indeed another uniquely determined value at the Thomas peak. In particular the authors find a resolution of the anomalous behaviour of the CDW1 approximation of the Thomas peak in that the catastrophic dip arising from the accidental degeneracy in CDW1 at the real Thomas angle is precisely eradicated by inclusion of CDW2. Moreover, they note that the magnitude of the 'interference minimum', which occurs near 0.6 times the Thomas angle, depends upon the theory adopted.