Relativistic ab initio calculation of the xenon 5s ionization spectra for the ( gamma,e) and (e,2e) reactions

Shake-Off Process in Non-Sequential Single-Photon Double Ionization of Closed-Shell Atomic Targets

Amusia and Kheifets in 1984 introduced a Green’s function formalism to describe the effect of many-electron correlation on the ionization spectra of atoms. Here, we exploit this formalism to model the shake-off (SO) process, leading to the non-sequential single-photon two-electron ionization (double photoionization—DPI) of closed-shell atomic targets. We separate the SO process from another knock-out (KO) mechanism of DPI and show the SO prevalence away from the DPI threshold. We use this kinematic regime to validate our model by making a comparison with more elaborate techniques, such as convergent and time-dependent close coupling. We also use our model to evaluate the attosecond time delay associated with the SO process. Typically, the SO is very fast, taking only a few attoseconds to complete. However, it can take much longer in the DPI of strongly correlated systems, such as the H− ion as well as the subvalent shells of the Ar and Xe atoms and Cl− ion.

Observation of giant resonance phenomena in the two-step mechanism of electron-Xe collision

We report an (e,2e) binding energy spectrum of Xe obtained at an impact energy of 2.1 keV, which covers the binding energy range up to 220 eV. The result is directly compared with data from high-energy photoelectron spectroscopy. It is found that an (e,2e)-specific, very broad band appears at around 120 eV, although in other energy regions the binding energy spectra by the two methods are in good agreement. The presence of such a band is revealed for the first time, which can be attributed to the second-order effects of the electron-target interaction that involves giant resonance phenomena of the Xe 4d electron.

Examination of (e,2e) scattering models by comparison of momentum profiles of noble gases between experiment and theory

Momentum profiles have been measured for the two outermost atomic orbitals of noble gases, Ar, Kr and Xe, at incident electron energy of about 2 keV using a newly developed multichannel (e,2e) spectrometer. The experimental results exhibit significantly improved statistics compared with those achieved in previous studies while covering a wide range of momenta up to 3.6 a.u. The results are compared with theoretical calculations using four (e,2e) scattering models, the plane-wave impulse and Born approximations (PWIA and PWBA), and the distorted-wave impulse and Born approximations (DWIA and DWBA). The DWIA and DWBA scattering models have been found to satisfactorily reproduce the experimental momentum profiles in terms of both shape and intensity over the entire momentum range covered, indicating the importance of distorted wave effects for quantitatively describing (e,2e) reaction.

Orbitals observed by Electron Momentum Spectroscopy

Numerical representations of Dyson orbitals can be extracted from the experimental data of electron momentum spectroscopy (EMS). These orbitals are solutions of the quasiparticle equation for the target electronic system. They closely obey the weak-coupling approximation. This defines a normalized Dyson orbital in terms of the sum of EMS cross sections for an orbital manifold of ion states whose momentum profiles have the same shape. Normalized Dyson orbitals are closely related to the orbitals of density functional theory. They are realistic in the sense that they give an independent-particle approximation to the target structure that reproduces experimental data, including molecular data obtained from experiments independent of EMS.