Impact Of Bare Ions Research Articles

Dynamic effective charge in the continuum final state in the CDW-EIS model: ionisation of molecules by bare-ion impact

Dynamic effective charge in the continuum final state in the CDW-EIS model: ionisation of molecules by bare-ion impact

Triple differential cross sections for single ionization of an atom by bare ion impact

We present triple differential cross sections (TDCSs) for single ionization of atoms by proton and highly charged bare ions impact by means of the three-body formalism of the first Born, two-Coulomb wave and three-Coulomb (3C) wave (3CW) methods, respectively. The TDCS has been calculated both in the scattering and perpendicular planes. The purpose of this work is to investigate the validity of different methods as well as the role of interaction between projectile and residual-target-ion in the final state for weak perturbation strength with low electron emission energy at several momentum transfers. By comparing our calculations with experimental data, overall, the 3CW predicts better agreement with experiments than other calculations in the scattering plane. In the perpendicular plane, all calculations deviate from experimental data with increasing transverse momentum transfer for p − He collision. At low momentum transfer, the location of binary peak obtained by the first Born approximation calculation is well established with the experiment for proton impact. On the other hand, the 3CW model is in much better agreement with experiments, both in absolute values and peak position for highly charged impact. Finally, the strong influence of the internuclear Coulomb distortion on TDCS has been observed at low and intermediate momentum transfer.

A Complete CDW Theory for the Single Ionization of Multielectronic Atoms by Bare Ion Impact

A complete form of the post version of the continuum distorted wave (CDW) theory is used to investigate the single ionization of multielectronic atoms by fast bare heavy ion beams. The influence of the non-ionized electrons on the dynamic evolution is included through a residual target potential considered as a non-Coulomb central potential through a GSZ parametric one. Divergences found in the transition amplitude containing the short-range part of the target potential are avoided by considering, in that term exclusively, an eikonal phase instead of the continuum factor as the initial channel distortion function. In this way, we achieve the inclusion of the interaction between the target active electron and the residual target, giving place to a more complete theory. The present analysis is supported by comparisons with existing experimental electron emission spectra and other distorted wave theories.

Distorted wave model for sub-shell electron capture cross sections of noble gases by bare ion impact

SynopsisElectron capture from noble gases (He, Ne and Ar) are investigated in the framework of the quantum-mechanical distorted wave model. In this model, we use an independent electron model taking particular care of the representation of the bound and continuum target states. The results for partial and total capture cross sections are compared with other theoretical calculations and experimental data. The present results are found to be in very good agreement with the available experimental findings.

Electron-capture Process Induced by Bare Ion Impact on Biological Targets

Electron-capture Process Induced by Bare Ion Impact on Biological Targets

Single-Capture Cross Sections from Biological Molecules and Noble Gases by Bare Ion Impact

In this work, we report theoretical electron capture cross sections for single-electron removal from molecules of biological interest and noble gases by bare ion (H+ and He2+) impact at energies ranging from 25 to 10,000 keV/amu. We use a distorted wave (DW) method where the intermediate continuum state of the active electron with the target ion has been taken into account. This method is developed within the framework of the independent electron model taking particular care of the representation of the bound continuum target states. Two different approximations have been considered for molecular targets: molecular representation of the bound-state target wavefunction and Bragg’s additivity rule. The molecular orbital for targets are described within the framework of the complete neglect of differential overlap (CNDO) method based on the linear combination of atomic orbital (LCAO) approximation. Using the DW method, we have also calculated the K-, L- and M- shell electron capture in collisions of bare ions with three noble gases He, Ne, and Ar respectively. Contributions from different molecular orbitals and different shells to the total cross sections (TCS) are studied. The preference of electron capture occurs in accordance as the binding energy of the active electron in molecular orbital and atomic shell. The maximum contributions to TCS for SC comes from the less bound electrons in repetitive orbitals, whereas the tightly bound electrons dominate the TCS at higher projectile energy regime. Variation of TCS with impact energy are compared with the available experimental observation and other theoretical findings. We find that the present theoretical method is satisfactory in both intermediate and high-energy region for molecules as well as noble gas targets to give reliable outcomes compared to other theoretical methods.

Fully differential cross sections for ionization of by ion impact: classical and quantum effects

Single ionization of molecular ions by impact of bare ions is theoretically studied. Fully differential cross sections are calculated by employing the prior version of the continuum distorted wave-eikonal initial state model within an independent electron approximation. It is shown in this work that, under certain conditions there can exist a competition between classical and quantum mechanisms in the ionization reaction that gives rise to the suppression of characteristic classical structures, namely the binary and recoil peaks, from the ionization angular spectra. The existence of destructive quantum interferences due to the coherent emission of electrons from the neighbourhood of both molecular centres may be held as the responsible for the suppression of these classical signatures. Different behaviours are observed depending on whether the ground (gerade) or the first excited (ungerade) states of the target are analysed. Different values of the projectile nuclear charge and collision geometries are considered when calculating FDCS.

Cross section scaling for H2O ionization by highly-charged ion impact

Electron production following single and multiple ionization of H2O by bare ion impact is theoretically studied by means of the classical trajectory Monte Carlo method. Our results are benchmarked against experimental data collected in different laboratories and other theoretical data obtained by means of distorted wave methods. In this work, the ten electrons in the molecule are explicitly considered, in contrast to previous formulations based on a single active electron description of the target. Present studies cover the energy range of (100 keV/amu)/Zp to (1000 keV/amu)/Zp, where Zp is the incident projectile charge. Projectile charges investigated ranged from 1+ to 13+. A simple scaling of the cross section is presented.

Energy and angular distribution of electrons ejected from water by the impact of fast O8+ ion beams

Double differential cross sections (DDCS) of electrons emitted from vapor water molecules (in vapor phase) by 2.0 MeV/u and 3.75 MeV/u bare oxygen ion impact have been measured by continuum electron spectroscopy technique. The ejected electrons were detected by an electrostatic hemispherical deflection analyzer over an energy range of 1–600 eV and emission angles from 20∘ to 160∘. The DDCS data has been compared with the continuum-distorted-wave-eikonal-initial state (CDW-EIS) approximation and a reasonable agreement was found with both version of the models i.e. post and prior version. By numerical integration of the DDCS data, the single differential cross section (SDCS) and total ionization cross section (TCS) were obtained. The obtained TCS results were compared with other available TCS results for water target within the same energy range. The total ionization cross sections values are seen to saturate as the projectile charge state (q p ) increases, which is in contrast to the first-Born predicted q p 2 dependence. This is also in contrast to the prediction of the CDW-EIS models.

Differential electron emission from polycyclic aromatic hydrocarbon molecules under fast ion impact

Interaction between polycyclic aromatic hydrocarbon (PAH) molecule and energetic ion is a subject of interest in different areas of modern physics. Here, we present measurements of energy and angular distributions of absolute double differential electron emission cross section for coronene (C24H12) and fluorene (C13H10) molecules under fast bare oxygen ion impact. For coronene, the angular distributions of the low energy electrons are quite different from that of simpler targets like Ne or CH4, which is not the case for fluorene. The behaviour of the higher electron energy distributions for both the targets are similar to that for simple targets. In case of coronene, a clear signature of plasmon resonance is observed in the analysis of forward-backward angular asymmetry of low energy electron emission. For fluorene, such signature is not identified probably due to lower oscillator strength of plasmon compared to the coronene. The theoretical calculation based on the first-order Born approximation with correct boundary conditions (CB1), in general, reproduced the experimental observations qualitatively, for both the molecules, except in the low energy region for coronene, which again indicates the role of collective excitation. Single differential and total cross sections are also deduced. An overall comparative study is presented.

Double differential distribution of electron emission in the ionization of water molecules by fast bare oxygen ions

The doubly differential distributions of low-energy electron emission in the ionization of water molecules under the impact of fast bare oxygen ions with energy of 48 MeV are measured. The measured data are compared with two quantum-mechanical models, i.e. the post and prior versions of the continuum distorted wave–eikonal initial state (CDW-EIS) approximation, and the first-order Born approximation with initial and final wavefunctions verifying correct boundary conditions (CB1). An overall excellent qualitative agreement is found between the data and the CDW-EIS models whereas the CB1 model showed substantial deviation. However, the detailed angular distributions display some discrepancies with both CDW-EIS models. The single differential and total cross-sections exhibit good agreement with the CDW-EIS models. The present detailed data set could also be used as an input for modeling highly charged ion induced radiation damage in living tissues, whose most abundant component is water. Similar measurements are also carried out for a projectile energy of 60 MeV. However, since the double differential cross-section data show similar results the details are not provided here, except for the total ionization cross-sections results.

Differential ionization of a one-electron target under bare-ion impact: Application to proton-impact ionization of atomic hydrogen

Differential ionization of a one-electron target under bare-ion impact: Application to proton-impact ionization of atomic hydrogen

Differential electron emission from multi-electronic targets under highly harged bare ion impact

SynopsisWe report a combined experimental and theoretical study of double differential electron emission in ionization of different multi-electronic atoms under fast highly charged bare ion impact. The main aim is to un-derstand the electron dynamics for these targets which is quite different from one or two electron systems.

Energy and angular distributions of electron emission from diatomic molecules by bare ion impact

The three-Coulomb wave model has been used extensively to study the energy and angular distributions of double-differential cross sections (DDCS) of electron emissions from hydrogen and nitrogen molecules by bare ion impact at intermediate and high energies. In the present model, we have expressed the molecular triple differential cross section in terms of the corresponding atomic triple differential cross section multiplied by the occupation number and the average Rayleigh interference factor, which accounts for the two-center interference effect. Here we have used an active electron approximation of the molecule as a whole in the initial channel. To account for the effect of passive electrons, we have constructed a model potential that satisfies the initial conditions and the corresponding wavefunction has been calculated from the model Hamiltonian of the active electron in the target. In the final channel, we have used a hydrogenic model with an effective nuclear charge that is calculated from its binding energy. In this model, the correlated motion of the particles in the exit channel of the reaction is considered by an adequate product of three-Coulomb functions. The emitted electron, the incident projectile ion and the residual ion are considered to be in same plane. The obtained results are compared with other recent theoretical and experimental findings. There is an overall agreement of the calculations with the experimental data for electron emission cross sections.

Single ionization of diatomic molecules by bare ion impact

The molecular three-Coulomb wave model (M3CW) has been extensively used to study the double-differential ionization cross sections (DDCS) of diatomic molecules by the impact of bare ions at intermediate and high energies. In this model, the distortion of the initial channel by the incoming projectile is also included. The present DDCS results are found to be in good accord both with the experiment of Baran et al 2008 as well as with other theory.

Dynamic electron screening in ionization of multi-shell atoms by bare ion impact

The influence of the electron dynamic screening on the single ionisation of atomic targets is studied by the comparisson of the post and prior forms of the CDW-EIS models. Also a complete-post version of the CDW-EIS approximation is presented. Theoretical results are shown together with existing experimental data.

Fully and double differential cross sections for the single ionization of H2O by bare ion impact

A theoretical study of fully differential cross sections for the single ionization of H2O by collisions with H+, and He2 + at an impact energy of 2 and 6 MeV amu−1 is presented. We work in terms of the Born-3DW model, which considers in the final state a model central potential to represent the interaction of the emitted electron with the molecular core. Results are presented for the lesser bound molecular orbitals (1B1, 1B2, 2A1 and 3A1). Doubly differential cross sections in terms of the electron emission angle are also presented for these molecular orbitals, showing a nearly isotropic distribution for the electron energies under consideration.

Double-differential cross sections for single ionization of helium by bare ion impact

Double-differential cross sections (DDCS) for single ionization of helium by impact of proton and highly charged carbon ion have been calculated in the framework of four-body formalism using the three-Coulomb wave model (3C-4B) and first Born approximation (FBA-4B), respectively. The correlated motion of the particles interacting through long-range Coulomb potential is properly taken into account in the final state. In this paper, the energy and angular distributions of DDCS of low- and high-energy electron emission for ground-state helium atoms have been investigated. The ejected electrons are affected by the two-center field of the target and the projectile ion. The two-center effects are confined to comparison with other theoretical results. The results obtained, both from the 3C-4B and FBA-4B models, are compared with other theoretical and experimental findings. The present results are found to reproduce the peak structure of the experimental observations. Large discrepancy occurs between the present two theories at forward and backward angles except about the emission angle 90°. The present computed results obtained by the 3C-4B model are in good agreement with the available experimental findings.

Double differential cross sections for ionization of water molecules by ion impact

Single ionization from water molecules by impact of bare ions is studied. Different approximations are employed, within the post and prior versions of the continuum distorted wave–eikonal initial state model, to calculate double differential cross sections. Post–prior discrepancies are observed between theoretical results. The sensitivity of the calculations to the description of the initial bound orbitals is investigated.

Electron double differential cross sections for ionization of O2 under fast C6+ ion impact and interference oscillation

The absolute double differential cross sections (DDCS) have been obtained for electron emission from oxygen molecules under the impact of bare carbon ions. The DDCS values are measured between an energy range of a few eV to 600 eV and over an angular range of 30–150°. These are then compared with the continuum distorted wave-eikonal initial state (CDW-EIS) calculations. The DDCS values for O2 are divided by that of atomic oxygen (calculated theoretically) to look for any oscillatory behaviour arising from Young-type interference. In addition, the DDCS ratios are further divided by a fitted straight line to extract any primary interference oscillation. Although a negative result has been obtained, these observations are in qualitative agreement with the prediction of the CDW-EIS model used.