Zehra Nur Ozer

Double Differential Cross-Sections for Electron Impact Ionization of Atoms and Molecules

The single ionizing collision between an incident electron and an atom/molecule ends up two kinds of outgoing electrons called scattered and ejected electrons. As features of electron impact ionization, these two types of electrons are indistinguishable. Double differential cross-sections (DDCS) can be obtained by measuring the energy and angular distributions of one of the two outgoing electrons with an electron analyzer. We used He, Ar, H2, and CH4 targets in order to understand the ionization mechanisms of atomic and molecular systems. We measured differential cross-sections (DCS) and double differential cross-sections at 250 eV electron impact energy. The elastic DCSs were measured for He, Ar, H2, and CH4, whereas the inelastic DCSs of He were obtained for 21P excitation level for 200 eV impact electron energy.

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.

Observation of two-center interference effects for electron impact ionization of N 2

In 1966, Cohen and Fano (1966 Phys. Rev. 150 30) suggested that one should be able to observe the equivalent of Young’s double slit interference if the double slits were replaced by a diatomic molecule. This suggestion inspired many experimental and theoretical studies searching for double slit interference effects both for photon and particle ionization of diatomic molecules. These effects turned out to be so small for particle ionization that this work proceeded slowly and evidence for interference effects were only found by looking at cross section ratios. Most of the early particle work concentrated on double differential cross sections for heavy particle scattering and the first evidence for two-center interference for electron-impact triple differential cross section (TDCS) did not appear until 2006 for ionization of H2. Subsequent work has now firmly established that two-center interference effects can be seen in the TDCS for electron-impact ionization of H2. However, in spite of several experimental and theoretical studies, similar effects have not been found for electron-impact ionization of N2. Here we report the first evidence for two-center interference for electron-impact ionization of N2.

Experimental and theoretical triple differential cross sections for electron-impact ionization of Ar (3p) for equal energy final state electrons

There have been several studies of electron-impact ionization of inert gases for asymmetric final state energy sharing and normally one electron has an energy significantly higher than the other. However, there have been relatively few studies examining equal energy final state electrons. Here we report experimental and theoretical triple differential cross sections for electron impact ionization of Ar (3p) for equal energy sharing of the outgoing electrons. Previous experimental results combined with some new measurements are compared with distorted wave born approximation (DWBA) results, DWBA results using the Ward–Macek (WM) approximation for the post collision interaction (PCI), and three-body distorted wave (3DW) which includes PCI without approximation. The results show that it is crucially important to include PCI in the calculation particularly for lower energies and that the WM approximation is valid only for high energies. The 3DW, on the other hand, is in reasonably good agreement with data down to fairly low energies.

Interference Effects for Intermediate Energy Electron-Impact Ionization of H 2 and N 2 Molecules

We have studied electron impact ionization of H2 and N2 molecules at intermediate energies to look for possible two center interference effects experimentally and theoretically. Here we report a study of the interference factor I for 250 eV electron-impact ionization. The experimental measurements are performed using a crossed-beam-type electron-electron coincidence spectrometer and theoretical calculations are obtained using the Molecular Three Body Distorted Wave Approximation (M3DW). We found that the I-factor demonstrated strong evidence for two-center interference effects for both H2 and N2. We also found that the I-factor is more sensitive to projectile angular scans than to ejected electron energy scans which indicate that for the present set of kinematics the diffraction of the projectile from two scattering centers is more important than interference between electron waves emitted from two different centers.

Young Double Slit Interference Effects at Quantum Level

The currently accepted model for quantum interference resulting from the emission of electron waves from two scattering centers induced by either light or charged particle impact is analogous to Youngs emission of two light waves from two slits. In this work we show that this simple classical wave model is incomplete and that there is a more complicated quantum interference pattern for low energy ionization caused by electron impact.

Theoretical and Experimental Studies on the Electron Impact Ionization of Helium at Intermediate Energies

In this work, triple differential cross section (TDCS) results on the electron impact ionization of He are presented. The experiments were performed in a coplanar asymmetric geometry with an incident electron energy of E0=250 eV and scattered electron angles (θs) of 7, 15, and 30˚, then compared with the theoretical calculations derived using the first and second Born approximations. The first Born term was calculated analytically, and the second Born term was determined in the closure approximation using semi-analytical calculations. The theoretical results were corrected by the so-called Gamow factor in order to include post-collision effects (PCI). A better agreement was found between the theoretical and experimental data for 7 and 30 degrees. As a result, we conclude that the inclusion of higher order effects is necessary to describe the ionization process.

Experimental and theoretical double differential cross sections for electron impact ionization of methane

Experimental and theoretical double differential cross sections (DDCSs) for electron-induced ionization of methane (CH4) are here reported for primary energies ranging from 50 eV to 350 eV and ejection angles between 25° and 130°. Experimental DDCSs are compared with theoretical predictions performed within the first Born approximation Coulomb wave. In this model, the initial molecular state is described by using single center wave functions, the incident (scattered) electron being described by a plane wave, while a Coulomb wave function is used for modeling the secondary ejected electron. A fairly good agreement may be observed between theory and experiment with nevertheless an expected systematic overestimation of the theory at low-ejection energies (<50 eV).

First Evidence of Interference effects in the ionization of N2 molecule

We will present an experimental and theoretical investigation of triple differential cross sections for electron- impact ionization of nitrogen molecules at intermediate energies. A discussion of interference effects contained in the theoretical and experimental interference factors will be presented.

Double Differential Cross Section Measurements for Electron Impact Ionization of Atmospheric Gases

We present comprehensive experimental measurements of double differential cross sections (DDCS) for atmospheric gases, Ar, N2, CO2 and CH4. DDCSs were obtained by measuring the energy and angular distributions of one of the two outgoing electrons which are indistinguishable by use traditional electron spectrometer with an electron analyzer.