Distorted-wave Model Research Articles

Electron-impact ionization ofNe(2p)andAr(3p)at intermediate energies: Role of the postcollision interaction

We present the absolute triple differential cross section (TDCS) for single ionization of $\mathrm{Ne}(2p)$ at an impact energy of 599.6 eV and $\mathrm{Ar}(3p)$ at 195 eV. The role of the postcollision interaction (PCI) is studied using a high-order distorted-wave Born approximation model with a continuum distorted-waves expansion. Both the second- and third-order effects are considered in the present calculations, and the third-order distorted wave Born approximation model is reported in the $(e,2e)$ reaction. The calculated results show satisfactory agreement with experimental data. The magnitude of the absolute TDCS is enhanced by a factor 2--3 when the strength factor $\ensuremath{\gamma}$ of the PCI amplitude is summarized just from 0 to 2. This proves that the PCI plays an important role in the absolute TDCS of the $(e,2e)$ reaction in the intermediate-energy region.

Single ionization of helium by 1-MeV protons

We consider the basic collision dynamics of single ionization of helium by 1-MeV protons using distorted-wave models and the first Born approximation. A good agreement is found between results of the distorted-wave models and recent experimental data [H. Gassert, O. Chuluunbaatar, M. Waitz et al., Phys. Rev. Lett. 116, 073201 (2016)] for electron emission into the azimuthal plane. However, unexpected discrepancies are observed between the theoretical results and the experimental data for the emission into the collision plane. Our consideration also shows that even though these collisions belong to the regime of weak perturbations, substantial differences exist between the results of the distorted-wave models and the first Born approximation.

Off-shell distortions of multichannel atomic processes

Any multichannel problem can be reduced to a succession of two-body events. However, these basic building blocks of many-body theories do not correspond to elastic processes but are off-the-energy-shell. In view of this difficulty, the great majority of the Distorted-Wave models includes a subsidiary approximation where these off-shell terms are arbitrarily forced to lie on the energy shell. At a first glance, since the energy deficiency is negligible for high enough velocities, the on-shell assumption seems to be completely justified. However, for the case of Coulomb interactions, the two-body off-shell distortions have branch-point singularities on the on-shell limit. In this article we demonstrate that these singularities might produce sizeable distortions of multiple scattering amplitudes, mainly when dealing with ion-ion collisions. Finally, we propose a method of including these distortions that might lead to better results that removing them completely.

Application of a post-collisional-interaction distorted-wave model for (e, 2e) of some atomic targets and methane

Recently Isik et al (2016 J. Phys B: At. Mol. Opt. Phys. 49 065203) performed measurements of the triple differential cross sections (TDCSs) of methane by electron impact. Their data clearly show that post-collisional interaction (PCI) effects are present in the angular distributions of ejected electrons. A model describing the ejected electron by a distorted wave and including PCI is applied for the single ionization of atomic targets and for methane. Extensive comparisons between this model and other previous models are made with available experiments.

Angular momentum and orientation effects in excitation-ionization collisions

We present theoretical fully differential cross sections (FDCS) for electron-impact excitation-ionization of helium in which the final state He+ ion is oriented in a particular direction. Specifically, we study the process for He+ ions in the 2p0 state. Using our 4-body distorted wave model, we show a strong dependence of the FDCS on the ion’s orientation and trace some unexpected structures in the FDCS to the L = 2 term in the partial wave expansion for the ionized electron. A comparison is drawn to the ionization of oriented Mg (3p0) atoms, and unlike that process, we find that for excitation-ionization angular momentum must be transferred from either the projectile or the target atom.

Experimental and theoretical triple-differential cross sections for tetrahydrofuran ionized by low-energy 26-eV-electron impact

We report an experimental and theoretical study of low-energy electron-impact ionization of tetrahydrofuran, which is a molecule of biological interest. The experiments were performed using an advanced reaction microscope specially built for electron-impact ionization studies. The theoretical calculations were performed within the molecular three-body distorted-wave model. Reasonably good agreement is found between experiment and theory.

Projectile interaction effects in out-of-plane excitation-ionization of helium

We present theoretical three-dimensional fully differential cross sections for electron-impact excitation-ionization of helium when the ionized electron is found outside of the scattering plane. Using our first born approximation and 4-body distorted wave models, we examine the effect of the projectile in the initial and final states. Our calculations show that the inclusion of projectile interactions results in an increase in the magnitude of the recoil lobe.

A study of the turn-up effect in the electron momentum spectroscopy

Recently, a number of electron momentum spectroscopy measurements for the ionization of atoms and molecules have shown that the triple differential cross section (TDCS) has an unexpected higher intensity in a low momentum regime (Brunger M J, Braidwood S W, Mc Carthy I E and Weigold E 1994 J. Phys. B: At. Mol. Opt. Phys. 27 L597, Hollebone B P, Neville J J, Zheng Y, Brion C E, Wang Y and Davidson E R 1995 Chem. Phys. 196 13, Brion C E, Zheng Y, Rolke J, Neville J J, McCarthy I E and Wang J 1998 J. Phys. B: At. Mol. Opt. Phys. 31 L223, Ren X G, Ning C G, Deng J K, Zhang S F, Su G L, Huang F and Li G Q 2005 Phys. Rev. Lett. 94 163201, Deng J K, et al 2001 J. Chem. Phys. 114 882, Ning C G, Ren X G, Deng J K, Su G L, Zhang S F and Li G Q 2006 Phys. Rev. A 73 022704). This surprising result is now called the turn-up effect. Our aim is to investigate such an effect by studying the case of the ionization of atomic hydrogen in an excited state using the 3C model (Brauner M, Briggs J S and Klar H 1989 J. Phys. B: At. Mol. Opt. Phys. 22 2265) which is able to describe all the measured results of the single ionization of atomic hydrogen in its ground state for an incident energy beyond 200 eV. A comparison is also made of the findings of the present method with those of the plane wave impulse approximation and distorted wave models.

Nucleus–Nucleus Effects in Fully Differential Cross Sections for Energetic C6+ +He Collisions with Small Momentum Transfer**Supported by the National Natural Science Foundation of China under Grant No 11274215, and the Natural Science Foundation of Shanxi Province under Grant No 2010011009.

The modified Coulomb–Born approximation with and without the internuclear interaction (MCB-NN and MCB) is used to calculate the fully differential cross sections (FDCS) for the single ionization of helium by 100 MeV/amu C6+ impact. The effects of the internuclear interaction on the FDCS are examined in geometries. The results are compared with experimental data and theoretical predictions from a three-body distorted-wave (3DW) model and a time-dependent close-coupling model. It is shown that the present MCB-NN results are in good agreement with the experiments in the scattering plane and the MCB results qualitatively reproduce the experimental structure outside the scattering plane. In particular, the MCB theory predicts the ‘double-peak’ structure in the perpendicular plane.

Relativistic effects in electron-capture to the continuum in 90 MeV/u U88+ +N2 collisions

SynopsisThe Continuum Distorted Wave (CDW) model is used to describe electron-capture to continuum cusp in 90 MeV/u U88+ + N2 collisions. Relativistic effects are studied considering Lorentz transformations on the electron kinematics.

How include properly the dynamic-screening into the post-version of the Continuum Distorted Wave model

SynopsisThe post-version of the Continuum Distorted Wave (CDW) model neglects a part of the active electron- residual target interaction which has been shown to play a major role in obtaining the doubly differential cross sections (DDCS) for electron ionization. In this work we properly include the dynamic screening into the CDW model showing its influence over the ionization DDCS for several collision systems.

A hybrid distorted wave model: a (almost) complete-post version of the CDW model for single ionization

A hybrid CDW-CDW-EIS model is developed in order to include the dynamic screening in the post CDW approximation for single ionization. Doubly differential cross sections for single ionization of water molecules are calculated and comparison with available experimental data and other theories are shown.

Triply differential (e,2e) studies of phenol.

We have measured (e,2e) triple differential cross sections (TDCS) for the electron-impact ionisation of phenol with coplanar asymmetrical kinematics for an incident electron energy of 250 eV. Experimental measurements of the angular distribution of the slow outgoing electrons at 20 eV are obtained when the incident electron scatters through angles of -5°, -10°, and -15°, respectively. The TDCS data are compared with calculations performed within the molecular 3-body distorted wave model. In this case, a mixed level of agreement, that was dependent on the kinematical condition being probed, was observed between the theoretical and experimental results in the binary peak region. The experimental intensity of the recoil features under all kinematical conditions was relatively small, but was still largely underestimated by the theoretical calculations.

Electron emission in collisions between dressed Alq+ ions with He targets

Experimental and theoretical results are presented for electron emission in collisions between dressed Alq+ ions and atomic He targets. The experimental data are compared with a four-body CTMC model and two distorted wave models, namely the CDW and CDW-EIS. The contribution to total electron emission spectra from the ionisation of each collision center and as well as the simultaneous ionisation can be assessed separately.

A dynamical (e,2e) investigation of the structurally related cyclic ethers tetrahydrofuran, tetrahydropyran, and 1,4-dioxane

Triple differential cross section measurements for the electron-impact ionization of the highest occupied molecular orbitals of tetrahydropyran and 1,4-dioxane are presented. For each molecule, experimental measurements were performed using the (e,2e) technique in asymmetric coplanar kinematics with an incident electron energy of 250 eV and an ejected electron energy of 20 eV. With the scattered electrons being detected at -5°, the angular distributions of the ejected electrons in the binary and recoil regions were observed. These measurements are compared with calculations performed within the molecular 3-body distorted wave model. Here, reasonable agreement was observed between the theoretical model and the experimental measurements. These measurements are compared with results from a recent study on tetrahydrofuran [D. B. Jones, J. D. Builth-Williams, S. M. Bellm, L. Chiari, C. G. Ning, H. Chaluvadi, B. Lohmann, O. Ingolfsson, D. Madison, and M. J. Brunger, Chem. Phys. Lett. 572, 32 (2013)] in order to evaluate the influence of structure on the dynamics of the ionization process across this series of cyclic ethers.

Comprehensive study of 3-body and 4-body models of single ionization of helium

The frozen core approximation has been successfully used for many years to model 4-body collisions as 3-body collisions. We present a comprehensive comparison of 3-body and 4-body models for the process of single ionization of helium by electron impact using our 4-body distorted wave model. Differences between the two models are observed in both magnitude and peak locations. We identify four possible sources for the discrepancies between the models, and isolate the specific physical causes of the discrepancies.

Experimental and theoretical investigation of (e, 2e) ionization of Ar(3p) in asymmetric kinematics at 200 eV

Experimental and theoretical studies of electron impact ionization of the 3p orbital of argon are reported. The relative triple-differential cross sections were measured in the coplanar asymmetric geometry. The experimental data at an incident electron energy of 200 eV, ejected electron energies of 15 and 20 eV, and scattering angles of −10°, −15°, and −20° were obtained using a conventional crossed-beam (e, 2e) spectrometer. The experimental data are compared with predictions from first- and second-order hybrid distorted-wave plus R-matrix models, as well as a fully nonperturbative B-spline R-matrix approach.

Low energy (e,2e) coincidence studies of NH3: Results from experiment and theory

Experimental and theoretical triple differential cross sections (TDCS) from ammonia are presented in the low energy regime with outgoing electron energies from 20 eV down to 1.5 eV. Ionization measurements from the 3a1, 1e1, and 2a1 molecular orbitals were taken in a coplanar geometry. Data from the 3a1 and 1e1 orbitals were also obtained in a perpendicular plane geometry. The data are compared to predictions from the distorted wave Born approximation and molecular-three-body distorted wave models. The cross sections for the 3a1 and 1e1 orbitals that have p-like character were found to be similar, and were different to that of the 2a1 orbital which has s-like character. These observations are not reproduced by theory, which predicts the structure of the TDCS for all orbitals should be similar. Comparisons are also made to results from experiment and theory for the iso-electronic targets neon and methane.

Distorted wave calculations for electron loss process induced by bare ion impact on biological targets

Distorted wave models are employed to investigate the electron loss process induced by bare ions on biological targets. The two main reactions which contribute to this process, namely, the single electron ionization as well as the single electron capture are here studied. In order to further assess the validity of the theoretical descriptions used, the influence of particular mechanisms are studied, like dynamic screening for the case of electron ionization and energy deposition on the target by the impacting projectile for the electron capture one. Results are compared with existing experimental data.

Double ionization of Helium by bare ions: theoretical study of the fully differential cross sections

In this work we study the double ionization of He induced by fully stripped projectiles. Distorted wave models based on effective charges which dynamically couple the two-body subsystems are compared to simpler models widely studied in the literature. The influence of the projectileś velocity and charge sign and magnitude on the fully differential cross sections (FDCS) are analyzed.