Continuum Distorted Wave-eikonal Initial State Model Research Articles

Electron emission from fluorene (C13H10) upon 3.5 MeV/u Si8+ ion impact: double differential distributions

We have studied the electron emission from one of the polycyclic aromatic hydrocarbon (PAH) molecules namely, fluorene (C13H10), upon 3.5 MeV/u Si8+ ion impact. The experimentally measured absolute double differential cross sections (DDCS) are compared with the continuum distorted wave-eikonal initial state (CDW-EIS) model and the first Born approximation including correct boundary conditions (CB1). The measurements are carried out in the ejected e−-energy range of 1 eV–400 eV and in the angular range of 20°–160°. We have obtained the single differential and the total cross sections (TCSs) of e−-emission as well. The CB1 calculation largely underestimates the data. The CDW-EIS model, which is applied for the PAH molecule for the first time, provides an overall better agreement with the double differential, single differential and TCS data. The DDCS data for fluorene has also been compared with that for CH4 molecule, at a few angles. The forward–backward angular asymmetry shows a relatively flatter distribution compared to the theoretical predictions. The contribution due to the giant plasmon resonance could not be clearly observed except a mild indication in the asymmetry parameter. The angular distribution of the carbon KLL Auger electron cross section shows certain variations. The study of the KLL hyper-satellite component indicates the double K-ionization cross section is about 8.6% of the single K-ionization one.

Ionization of atoms and molecules using 200-keV protons and 5.5-MeV/u bare C ions: Energy-dependent collision dynamics

Using electron spectroscopy technique, we measure the absolute double-differential cross sections (DDCSs) of electrons emitted in collisions of 200-keV protons on He, ${\mathrm{CH}}_{4}$, and ${\mathrm{O}}_{2}$ and 5.5-MeV/u bare C ions colliding on ${\mathrm{O}}_{2}$. The emitted electrons are measured in the energy range from 1 to 400 eV for He and ${\mathrm{CH}}_{4}$ targets and up to 600 eV for ${\mathrm{O}}_{2}$ to include the $K\text{\ensuremath{-}}LL$ Auger line of oxygen. The electrons are detected over different emission angles varying from ${20}^{\ensuremath{\circ}}$ in the extreme forward direction to ${160}^{\ensuremath{\circ}}$ in the backward direction. The single-differential cross section (SDCS) and total cross section are deduced from the measured DDCSs spectra for all the targets. The DDCS and SDCS are compared with the state-of-the-art continuum distorted wave--eikonal initial state (CDW-EIS) theoretical model. The CDW-EIS model provides excellent agreement with the oxygen data at MeV energy, whereas the deviation in the case of keV energy is substantial, in spite of having nearly the same perturbation strength. The forward-backward angular asymmetry shows a saturation effect in the case of keV energy protons but no such signature is observed for the high-energy collision. A systematic analysis reveals that the asymmetry at low electron energy is sensitive to the associated atomic or molecular structure and is in close agreement with the theory.

Double-differential cross sections for ionization of H2O by fast bare O ions: Comparison with continuum-distorted-wave eikonal-initial-state calculations in prior and post forms

We have measured the double-differential cross sections (DDCS) for electron emission in ionization of H2O molecules under the impact of 4.5-MeV/ uO 8+ ions. The data were collected between 1 and 600 eV, in an angular range of 20 ◦ –150 ◦ by using an electrostatic hemispherical analyzer. In the experiment we used the H2O vapor in a static gas condition which allowed us to deduce the absolute value of the cross sections. The single-differential cross sections (SDCS) and the total cross sections have also been obtained. The DDCS as well as the SDCS spectra are compared with the continuum-distorted-wave eikonal-initial-state (CDW-EIS) calculations for both the prior as well as the post forms of the scattering matrix. The initial state is represented within the complete neglect of differential overlap approximation, where the molecular orbitals are expressed in terms of atomic orbitals of the atomic constituents. The overall agreement with the CDW-EIS model is quite good as far as the energy dependence is concerned. The prior form of the model is found to provide a better understanding of the data compared to the post version. In particular, excellent agreement between the theory and experiment has been observed for the angular distribution data at forward angles.

Energy and angular distributions of the low-energy electron emission in collisions of 4 MeV/u bare F ions with He atoms

The energy and angular distributions of double-differential cross sections (DDCS) of electron emission from He in collisions with 4 MeV/u F9 + ions are reported. The derived single-differential distributions and the total cross sections are also reported. The measured distributions of the low-energy electrons between 1 and 400 eV over a wide angular range between 20° and 160° are compared with the state-of-the-art quantum mechanical models. The first Born (B1) and the continuum distorted wave-eikonal initial state (CDW-EIS) approximations are used for this purpose. The DDCS for a given angle was found to fall by a few orders of magnitude over the electron energy range studied. The CDW-EIS model provides excellent agreement with the energy distributions and the angular distributions. The electron energy dependence of the forward–backward asymmetry parameter shows monotonically increasing behaviour. This has been explained very well in terms of the CDW-EIS model, which includes the two-centre effect. A large deviation from the B1 is also observed. We have also derived the single-differential distributions in terms of the angle as well as the electron energy. These distributions are also well reproduced by the CDW-EIS model.

Ionization of molecular hydrogen by 5 MeV/u bare fluorine ion and electron interference

Electrons emitted from H2 in collisions with 5 MeV/u F9 + ions were measured in the energy range from 1 to 300 eV and a wide range of emission angles between 20° and 160°. The measured energy and angular distributions of double-differential cross sections (DDCSs) of these electrons are compared with the molecular continuum distorted wave-eikonal initial state (CDW-EIS) calculation. The observed energy and angular distributions can be explained, in general, with the help of the two-centre effect which is included in the CDW-EIS model. In addition, the DDCS ratios of molecular-to-atomic hydrogen exhibit an oscillatory structure which is discussed in terms of Young-type electron interference. We have obtained the frequencies of such oscillations and studied their angular dependence. The single-differential cross sections (SDCSs) are deduced by integrating the DDCSs over solid angle and emission energy. We demonstrate that the SDCS ratio spectra also preserve the signature of interference to some extent. The asymmetry parameter, derived only from the molecular cross sections for forward and backward angles, shows an oscillatory behaviour as a function of electron velocity. This is understood in terms of the interference effect superimposed with the post-collisional two-centre effect.

Single ionization of Ne, Ar and Kr by proton impact: Single differential distributions in energy and angle

In this work we present a theoretical study of singly differential cross sections in energy and angle for the single ionization of neon, argon and krypton by proton impact. Theoretical results obtained by means of the Continuum Distorted Wave-Eikonal initial state (CDW-EIS) model are compared to those provided by the First Born Approximation (FBA) and the classical trajectory Monte Carlo (CTMC) method as well as to experimental data from several laboratories. We note in particular for argon, that the CDW-EIS model does not reproduce the experimental data as accurately as expected, while the CTMC instead is in very good agreement.

Interference pattern signatures in fully differential cross sections for single ionization of H2 molecules by fast protons

Electron interference signatures present in fully differential cross sections for single ionization by 6 MeV protons in H2 molecules are investigated. We employ a molecular version of the continuum-distorted wave-eikonal initial state model, where all the interactions present in the exit channel are considered on an equal footing. Calculations of fully differential cross sections are performed for different electron and projectile kinematical conditions and the range of validity of the theoretical approach is discussed. Furthermore, we explore the presence of interference patterns in differential cross sections for both aligned and randomly oriented targets in asymmetric coplanar geometries.