Target dependence of post-collision effects in ionization by proton impact

Abstract

We have measured and calculated double differential cross sections for ionization of Ne and Ar by 75 keV proton impact for a broad range of fixed projectile energy losses as a function of scattering angle. Along with data obtained previously for lighter targets this made possible a systematic analysis of post-collision effects between the scattered projectile and the continuum electron in the exit channel as a function of the target ionization potential. The data are consistent with an increasing strength of such effects with increasing ionization potential. However, second-order effects involving the projectile—residual target ion interaction also play an important role.

Target dependence of postcollision interaction effects on fully differential ionization cross sections

“…If this is indeed the case one would have to conclude that near the cusp energy PCI proceeds mostly through the V pe -V te -V pe sequence and that the V pe -V pt -V pe sequence is overestimated in the CDW-EIS-PT and 3DW-EIS models. Indications for such an overestimation were also found in the FDCS for ionization of H 2 [24] and in the DDCS for ionization of Ne and Ar [33].…”

“…Instead, measured DDCS as a function of projectile energy loss and scattering angle seemed to suggest that PCI actually becomes stronger with decreasing I [16,27]. On the other hand, as mentioned in the introduction, a follow-up study on DDCS for heavier targets [33] suggested that effects due to PCI could be masked by those due to another higher-order mechanism, involving the PT interaction, but only a single projectile-electron interaction (for simplicity, we refer to this process as the second-order PT process). Therefore, the dependence of PCI effects on I could not be conclusively determined from DDCS measurements.…”

“…Further signatures of PCI, which are not fully understood, were found in double differential cross sections (DDCS) as a function of scattering angle, which were measured for a broad range of ejected electron energies and for several target species [33]. For ejected electron energies below the velocity matching regime focusing effects due to PCI appeared to become increasingly pronounced with increasing target ionization potential I, which is the expected and theoretically predicted trend [24].…”

“…It is thus possible that PCI increases with increasing I even at the velocity matching, but that it is masked by the higher-order mechanism involving the PT interaction. The results of [24] and [33] show that our understanding of the few-body dynamics in this regime is much less complete than it is for electron energies well below the velocity-matching regime. Furthermore, for electrons much faster than the projectiles no experimental FDCS have been reported at all yet.…”

Double differential cross sections for ionization of H by 75 keV proton impact: Assessing the role of correlated wave functions*

“…Significant differences between theory and experiment were found. [3,25,26] This shows that in the region of electron-projectile velocity-matching, the differential cross section is very sensitive to the details of the underlying few-body dynamics. The research of this kind of situation has aroused the great interest of more and more experimental and theoretical workers.…”