Title: Projectile Coherence Effects in Twisted Electron Ionization of Helium
Over the last decade, it has become clear that for heavy ion projectiles, the projectile’s transverse coherence length must be considered in theoretical models. While traditional scattering theory often assumes that the projectile has an infinite coherence length, many studies have demonstrated that the effect of projectile coherence cannot be ignored, even when the projectile-target interaction is within the perturbative regime. This has led to a surge in studies that examine the effects of the projectile’s coherence length. Heavy-ion collisions are particularly well-suited to this because the projectile’s momentum can be large, leading to a small deBroglie wavelength. In contrast, electron projectiles that have larger deBroglie wavelengths and coherence effects can usually be safely ignored. However, the recent demonstration of sculpted electron wave packets opens the door to studying projectile coherence effects in electron-impact collisions. We report here theoretical triple differential cross-sections (TDCSs) for the electron-impact ionization of helium using Bessel and Laguerre-Gauss projectiles. We show that the projectile’s transverse coherence length affects the shape and magnitude of the TDCSs and that the atomic target’s position within the projectile beam plays a significant role in the probability of ionization. We also demonstrate that projectiles with large coherence lengths result in cross-sections that more closely resemble their fully coherent counterparts. more »« less
We have measured differential yields for double capture and double capture accompanied by ionization in 75 keV p + Ar collisions. Data were taken for two different transverse projectile coherence lengths. A small effect of the projectile coherence properties on the yields were found for double capture, but not for double capture plus ionization. The results suggest that multiple projectile–target interactions can lead to a significant weakening of projectile coherence effects.
Plumadore, A; Harris, A L
(, Journal of Physics B: Atomic, Molecular and Optical Physics)
Abstract Ionization collisions have important consequences in many physical phenomena, and the mechanism that leads to ionization is not universal. Double differential cross sections (DDCSs) are often used to identify ionization mechanisms because they exhibit features that distinguish close collisions from grazing collisions. In the angular DDCS, a sharp peak indicates ionization through a close binary collision, while a broad angular distribution points to a grazing collision. In the DDCS energy spectrum, electrons ejected through a binary encounter collision result in a peak at an energy predicted from momentum conservation. These insights into ionization processes are well-established for plane wave projectiles. However, the recent development of sculpted particle wave packets reopens the question of how ionization occurs for these new particle wave forms. We present theoretical DDCSs for (e, 2e) ionization of atomic hydrogen for electron vortex projectiles. Our results predict that the ionization mechanism for vortex projectiles is similar to that of non-vortex projectiles, but that the projectile’s momentum uncertainty causes noticeable changes to the shape and magnitude of the vortex DDCSs. Specifically, there is a broadening and splitting of the angular DDCS peak for vortex projectiles, and an increase in the cross section for high energy ejected electrons.
Smucker, J.; Montgomery, J. A.; Bredice, M.; Rozman, M. G.; Côté, R.; Sadeghpour, H. R.; Vrinceanu, D.; Kharchenko, V.
(, The Journal of Chemical Physics)
A semiclassical model describing the charge transfer collisions of C 60 fullerene with different slow ions has been developed to analyze available observations. These data reveal multiple Breit–Wigner-like peaks in the cross sections, with subsequent peaks of reactive cross sections decreasing in magnitude. Calculations of charge transfer probabilities, quasi-resonant cross sections, and cross sections for reactive collisions have been performed using semiempirical interaction potentials between fullerenes and ion projectiles. All computations have been carried out with realistic wave functions for C 60 ’s valence electrons derived from the simplified jellium model. The quality of these electron wave functions has been successfully verified by comparing theoretical calculations and experimental data on the small angle cross sections of resonant [Formula: see text] collisions. Using the semiempirical potentials to describe resonant scattering phenomena in C 60 collisions with ions and Landau–Zener charge transfer theory, we calculated theoretical cross sections for various C 60 charge transfer and fragmentation reactions which agree with experiments.
Radiative double-electron capture (RDEC), in which two-electron capture is accompanied by simultaneousemission of a single photon, was investigated for fully stripped and one-electron projectiles colliding withgaseous and thin-foil targets. RDEC can be considered the inverse of double photoionization by a single photon.For the gaseous targets, measurements were done for 2.11 MeV/uF9+and F8+ions interacting with N2and Ne,while for the thin-foil target the measurements were done for 2.11 MeV/uF9+and F8+and 2.19 MeV/uO8+andO7+ions striking thin C targets. Reports on this work were already published separately in shorter accounts by LaMantiaet al.[Phys. Rev. Lett.124, 133401 (2020)for the gas targets andPhys.Rev.A102, 060801(R) (2020)forthe thin-foil targets]. The gas targets were studied under single-collision conditions, while the foil targets sufferedunavoidable multiple collisions. The measurements were carried out by detecting x-ray emission from the targetat 90◦to the beam direction in coincidence with outgoing ions undergoing double, single, and, in the caseof the foil targets, no charge change inside the target. Striking differences between the gaseous and foil targetswere found from these measurements, with RDEC for the gaseous targets occurring only in coincidence with q-2outgoing projectiles as expected, while RDEC for the foil targets was seen in each of the outgoing q-2, q-1, and nocharge-change states. The no charge-change result was totally unexpected. The cross sections for RDEC for thefully stripped ions on gas targets were found to be about six times larger than those for the one-electron projec-tiles. For the foil targets, the RDEC cross sections for the fully stripped and one-electron projectiles differ some-what from one another but not to the the extent they did for the gas targets. In this work the cross sections for allof the projectiles for the foil targets were adjusted due to the target contaminant background from potassium andcalcium atoms that existed in the spectra. Also, the cross sections for the incident one-electron projectiles weremodified due to a correction for the fraction of these ions that becomes fully stripped in passage through the foil.These differences are attributed to the effects of the multiple collisions that occur for the foil targets. The differ-ential cross sections at 90◦determined for each of the projectiles interacting with each of the targets are comparedwith each other and with the previous measurements. To the extent that the cross sections follow a sin2θdepen-dence, the total cross sections are compared with theoretical calculations [E. A. Mistonova and O. Yu. Andreev,Phys. Rev. A87, 034702 (2013)], for which the agreement is poor, with the measured cross section exceedingthe predicted ones by about an order of magnitude. Possible reasons for this discrepancy will be discussed.
Radiative double electron capture (RDEC), occurring when two electrons are captured to a projectile ion with the simultaneous emission of a single photon, has been investigated. RDEC can be considered as the time inverse process of double photoionization. Strong evidence for RDEC is found in F9++ N2collisions and additionally for one‐electron F8+for which the probability for the process is expected to be considerably smaller. Preliminary values for the cross sections for RDEC have been determined. A significant advantage of the gas target is that multiple‐collision effects seen for a solid target are avoided due to the single‐collision conditions that prevail for gas targets.
Harris, A. L. Projectile Coherence Effects in Twisted Electron Ionization of Helium. Retrieved from https://par.nsf.gov/biblio/10475869. Atoms 11.5 Web. doi:10.3390/atoms11050079.
Harris, A. L. Projectile Coherence Effects in Twisted Electron Ionization of Helium. Atoms, 11 (5). Retrieved from https://par.nsf.gov/biblio/10475869. https://doi.org/10.3390/atoms11050079
@article{osti_10475869,
place = {Country unknown/Code not available},
title = {Projectile Coherence Effects in Twisted Electron Ionization of Helium},
url = {https://par.nsf.gov/biblio/10475869},
DOI = {10.3390/atoms11050079},
abstractNote = {Over the last decade, it has become clear that for heavy ion projectiles, the projectile’s transverse coherence length must be considered in theoretical models. While traditional scattering theory often assumes that the projectile has an infinite coherence length, many studies have demonstrated that the effect of projectile coherence cannot be ignored, even when the projectile-target interaction is within the perturbative regime. This has led to a surge in studies that examine the effects of the projectile’s coherence length. Heavy-ion collisions are particularly well-suited to this because the projectile’s momentum can be large, leading to a small deBroglie wavelength. In contrast, electron projectiles that have larger deBroglie wavelengths and coherence effects can usually be safely ignored. However, the recent demonstration of sculpted electron wave packets opens the door to studying projectile coherence effects in electron-impact collisions. We report here theoretical triple differential cross-sections (TDCSs) for the electron-impact ionization of helium using Bessel and Laguerre-Gauss projectiles. We show that the projectile’s transverse coherence length affects the shape and magnitude of the TDCSs and that the atomic target’s position within the projectile beam plays a significant role in the probability of ionization. We also demonstrate that projectiles with large coherence lengths result in cross-sections that more closely resemble their fully coherent counterparts.},
journal = {Atoms},
volume = {11},
number = {5},
publisher = {MDPI},
author = {Harris, A. L.},
}
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