Diffraction in the binary encounter electron peak observed in collisions of 0.6 MeV amu^-1I⁷⁺I²³⁺and Au¹¹⁺projectiles with He and Ar

Abstract

Relative double differential cross sections for electron emission from collisions of 0.6 MeV amu-1 I7+ and I23+ projectiles with Ar and Au11+ projectiles with He were measured for electron energies from 100 eV to 2000 eV and for angles from 0' to 50'. Experimentally observed sudden shifts of the position of the binary encounter peak were interpreted as resulting from quantum interference in the scattering of target electrons from the partially stripped projectile ion. To this end calculations for the elastic scattering of free electrons initially at rest in the laboratory reference frame from the screened projectile field as well as model calculations of binary encounter electron production taking into account the target Compton profile were performed and compared with the experimental results. Good agreement was obtained for the angular locations of these shifts as well as for the angular distribution of the binary encounter electron yield.

A quasielastic scattering approximation for target ionisation by heavy structured projectiles

“…Another deviation from first-order Born predictions is the peak shift to energies below Ef for bare [8] and few-electron projectiles [3], but also for multi-electron projectiles at collision velocities where structures are absent [4,7]. For systems with a doublepeak structure, the two peaks show hardly any variation with angle [5].…”

“…In the case of ionic projectiles, the actual calculations are usually performed with the on-shell formula (4.1) instead [5,21]. It should be pointed out, however, that for carrying out the step from (4.3) to (4.1), a channel distortion formalism [15] has to be employed when the projectile fields are of long range.…”

“…For projectiles carrying electrons, the BE electrons have shown a series of unexpected features. The most important ones are the violation of the Born scaling of the differential cross section with the square of the ionic projectile charge [1~2, 6,7] and the presence of binary encounter peak structures for very heavy projectiles with many electrons [4,5]. Another deviation from first-order Born predictions is the peak shift to energies below Ef for bare [8] and few-electron projectiles [3], but also for multi-electron projectiles at collision velocities where structures are absent [4,7].…”

“…The heavy projectiles (0.6MeV/amu Au 11+, 1 MeV/amu Au 12+ and 6 MeV/amu U 38+ on He) are investigated in Sect. 6 and compared to experiment [5,7,23,243. Binary encounter peak structures which appear for low charge states and small collision velocities are studied and related to the Ramsauer-Townsend minima in elastic electron-ion scattering [11].…”

The importance of continuum eigenstates in electron spectroscopy

“…Since for such fast electrons the final-state interaction with the target field is rather weak, the gross features of the BE peak can be reproduced with the plane wave Born approximation. However, a series of recent experimental investigations on the precise peak position [4,5] and the discovery of a double-peak structure for very heavy projectiles [6,7] demonstrate that the final-state interaction with the projectile cannot be neglected [8].…”