Outgoing Electrons Research Articles

Recent advances in relativistic excitation of atomic hydrogen

Within the framework of the relativistic regime ( E k > 2700 eV) and the first Born approximation, we investigate the inelastic excitation of atomic hydrogen by electron impact from 1 s to 2 p state. The incoming and outgoing electrons are described by free Dirac spinors, while the hydrogen atom target is described by the exact solutions of Dirac equation with a central potential. A detailed study has been devoted to the non-relativistic regime as well as the relativistic regime of the process, and the results obtained show the differences between the two regimes. These differences have revealed that the differential cross section (DCS) is influenced by the parameters of the 1 s and 2 p states, along with significant effects on diffusion during small pulse transfers. The relativistic effects are responsible for the significant changes in the DCS as a function of diffusion angles which depend on the chosen geometry.

On the characteristic features of ionization in QED environments.

The ionization of molecular systems is important in many chemical processes, such as electron transfer and hot electron injection. Strong coupling between molecules and quantized fields (e.g., inside optical cavities) represents a new promising way to modify molecular properties in a non-invasive way. Recently, strong light-matter coupling has shown the potential to significantly improve the rates of hot electron driven processes, for instance, in water splitting. In this paper, we demonstrate that inside an optical cavity, the residual interaction between an outgoing free electron and the vacuum field is significant. We further show that since the quantized field is also interacting with the ionized molecule, the free electron and the molecular system are correlated. We develop a theoretical framework to account for the field induced correlation and show that the interaction between the free electron and the field, free electron-field interaction, has sizable effects on the ionization potential of typical organic molecules.

Core-Level Spectroscopy of 2-Thiouracil at the Sulfur L1- and L2,3-Edges Utilizing a SASE Free-Electron Laser.

In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1- and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster–Kronig and Auger–Meitner emission at the L1- and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy.

Triple-differential cross sections for (e,2e) electron-impact ionization dynamics of tetrahydrofuran at low projectile energy

We study the triple-differential cross section (TDCS) for the electron-impact ionization of the highest occupied molecular orbital of tetrahydrofuran at a projectile energy ${E}_{0}=91\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$. The experimental data were measured using a reaction microscope, which covers a large part of the full solid angle for the secondary electron emission with energies ranging from 6 to 15 eV, and projectile scattering angles ranging from $\ensuremath{-}{10}^{\ensuremath{\circ}}$ to $\ensuremath{-}{20}^{\ensuremath{\circ}}$. The experimental TDCSs are internormalized across all measured scattering angles and ejected energies. They are compared with predictions from the multicenter distorted-wave (MCDW) approximation and a modified MCDW-Nee method which includes the postcollision interaction (PCI) using the Ward-Macek factor. Additional calculations were obtained using a molecular three-body distorted-wave (M3DW) approach which accounts for PCI in an exact treatment. Generally, the MCDW-Nee and M3DW models show better agreement with experiment than the MCDW calculations. This shows the importance of accounting for PCI for low-energy outgoing electrons in electron-impact ionization processes.

Reactivity and Lability Modulated by a Valence Electron Moving in and out of 25-Atom Gold Nanoclusters.

The emergence of atomically precise metal nanoclusters with unique electronic structures provides access to currently inaccessible catalytic challenges at the single-electron level. We investigate the catalytic behavior of gold Au25 (SR)18 nanoclusters by monitoring an incoming and outgoing free valence electron of Au 6s1 . Distinct performances are revealed: Au25 (SR)18 - is generated upon donation of an electron to neutral Au25 (SR)18 0 and this is associated with a loss in reactivity, whereas Au25 (SR)18 + is generated from dislodgment of an electron from neutral Au25 (SR)18 0 with a loss in stability. The reactivity diversity of the three Au25 (SR)18 clusters stems from different affinities with reactants and the extent of intramolecular charge migration during the reactions, which are closely associated with the valence occupancies of the clusters varied by one electron. The stability difference in the three clusters is attributed to their different equilibria, which are established between the AuSR dissociation and polymerization influenced by one electron.

Reactivity and Lability Modulated by a Valence Electron Moving in and out of 25‐Atom Gold Nanoclusters

AbstractThe emergence of atomically precise metal nanoclusters with unique electronic structures provides access to currently inaccessible catalytic challenges at the single‐electron level. We investigate the catalytic behavior of gold Au25(SR)18 nanoclusters by monitoring an incoming and outgoing free valence electron of Au 6s1. Distinct performances are revealed: Au25(SR)18− is generated upon donation of an electron to neutral Au25(SR)180 and this is associated with a loss in reactivity, whereas Au25(SR)18+ is generated from dislodgment of an electron from neutral Au25(SR)180 with a loss in stability. The reactivity diversity of the three Au25(SR)18 clusters stems from different affinities with reactants and the extent of intramolecular charge migration during the reactions, which are closely associated with the valence occupancies of the clusters varied by one electron. The stability difference in the three clusters is attributed to their different equilibria, which are established between the AuSR dissociation and polymerization influenced by one electron.

Transmitting the quantum state of electrons across a metallic island with Coulomb interaction.

The Coulomb interaction generally limits the quantum propagation of electrons. However, it can also provide a mechanism to transfer their quantum state over larger distances. Here, we demonstrate such a form of electron teleportation across a metallic island. This effect originates from the low-temperature freezing of the island's charge Q which, in the presence of a single connected electronic channel, enforces a one-to-one correspondence between incoming and outgoing electrons. Such faithful quantum state imprinting is established between well-separated injection and emission locations and evidenced through two-path interferences in the integer quantum Hall regime. The additional quantum phase of 2πQ/e, where e is the electron charge, may allow for decoherence-free entanglement of propagating electrons, and notably of flying qubits.

Does Spacecraft Potential Depend on the Ambient Electron Density?

In this paper, we address the question of whether spacecraft potential depends on the ambient electron density. In Maxwellian space plasmas, the onset of spacecraft charging does not depend on the ambient electron density. The balance of electron currents causes the incoming electrons to balance with the outgoing secondary electrons. The onset is controlled by the critical or anticritical temperature of the ambient electrons, but not the electron density. Above the critical temperature, charging to negative potential occurs. If the energy of the incoming electrons increases to well beyond the second crossing point of the secondary electron yield (SEY), the value of SEY decreases to well below unity. When the secondary electron current is negligible compared with the primary electron current, the spacecraft potential is governed solely by the balance of the incoming electrons and the sum of the currents of the repelled electrons and the attracted ions. In neutral space plasma, the electron and ion charges cancel each other. But if the space plasma deviates from being neutral, then the densities can have effect on the spacecraft potential. If the ambient plasma deviates significantly from equilibrium, a non-Maxwellian electron distribution may result. For a kappa distribution, one can show that the spacecraft charging level is independent of the ambient electron density. For a double Maxwellian distribution, the spacecraft charging level depends on the electron densities. For a conducting spacecraft charging in sunlight, the charging level is low and positive. It also depends on the ambient electron density. For a dielectric spacecraft in sunlight, the high-level negative-voltage charging on the shadowed side may extend to the sunlit side and block the photoelectrons trying to escape from the sunlit side. In this case, the charging level does not depend on ambient electron density. Using coordinated environmental and spacecraft charging data obtained from the Los Alamos National Laboratory geosynchronous satellites, we showed some results confirming that spacecraft potential is indeed often independent of the ambient electron density.

Laser-assisted electron momentum spectroscopy of

SynopsisElectron impact ionization of the hydrogen molecular ion in the presence of laser radiation is studied theoretically. The kinematical regime of high impact energy and large momentum transfer is considered. The influence of a laser field on the target is taken into account using a quasistatic states model, whereas its effect on the incoming and outgoing electrons is described by the Volkov functions. For the field-dressed target, the molecular bond oscillation factor, extracted from the electron momentum distribution, demonstrates a significantly different behavior compared to the case of the unperturbed target.

Dynamics of photoionization from molecular electronic wavepacket states in intense pulse laser fields: A nonadiabatic electron wavepacket study.

A theory for dynamics of molecular photoionization from nonadiabatic electron wavepackets driven by intense pulse lasers is proposed. Time evolution of photoelectron distribution is evaluated in terms of out-going electron flux (current of the probability density of electrons) that has kinetic energy high enough to recede from the molecular system. The relevant electron flux is in turn evaluated with the complex-valued electronic wavefunctions that are time evolved in nonadiabatic electron wavepacket dynamics in laser fields. To uniquely rebuild such wavefunctions with its electronic population being lost by ionization, we adopt the complex-valued natural orbitals emerging from the electron density as building blocks of the total wavefunction. The method has been implemented into a quantum chemistry code, which is based on configuration state mixing for polyatomic molecules. Some of the practical aspects needed for its application will be presented. As a first illustrative example, we show the results of hydrogen molecule and its isotope substitutes (HD and DD), which are photoionized by a two-cycle pulse laser. Photon emission spectrum associated with above threshold ionization is also shown. Another example is taken from photoionization dynamics from an excited state of a water molecule. Qualitatively significant effects of nonadiabatic interaction on the photoelectron spectrum are demonstrated.

Electron momentum spectroscopy of H+ 2 in the presence of laser radiation*

Theoretical analysis of laser-assisted electron impact ionization of a hydrogen molecular ion H+ 2 at high impact energy and large momentum transfer is carried out. The laser-field effects on the incoming and outgoing electrons are taken into account using the Volkov functions. The field-dressing of the target electron is treated with a quasistatic state approach. Calculations for laser radiation with frequency ω = 1.55 eV and intensity I = 5 × 1011 W/cm2 exhibit strong laser influence on the molecular bond oscillation in laser-assisted electron momentum distributions.

Electric dipole excitation of 208Pb by polarized electron impact

The cross sections and spin asymmetries for the excitation of 1- states in 208Pb by transversely polarized electrons with collision energy of 30-180MeV have been examined within the DWBA scattering formalism. As examples, we have considered a low-lying 1- state and also states belonging to the pygmy dipole and giant dipole resonances. The structure of these states and their corresponding transition charge and current densities have been taken from an RPA calculation within the quasiparticle phonon model. The complex-plane rotation method has been applied to achieve the convergence of the radial DWBA integrals for backward scattering. We have studied the behaviour of the cross sections and spin asymmetries as a function of electron energy and scattering angle. The role of the longitudinal and transversal contributions to the excitation has been thoroughly studied. We conclude that the spin asymmetry S, related to unpolarized outgoing electrons, is mostly well below 1% even at the backward scattering angles and its measurement provides a challenge for future experiments with polarized electrons.

Plasma wakefield acceleration shows promise

When electrons are precisely positioned in a region of high electric field, they can pick up a lot of energy in a small space.

Multicenter distorted-wave method for fast-electron-impact single ionization of molecules

A multicenter distorted-wave (MCDW) method for fast-electron-impact single ionization of a molecular system in the coplanar-asymmetric kinematics is developed. Plane waves are used to describe the fast incoming and outgoing electrons and the multicenter nature of the molecule is considered by describing the slow ejected electron with the multicenter distorted wave, which is solved from the anisotropic multicenter potential between the ejected electron and the ionic molecule. The MCDW method improves the conventional molecular distorted-wave methods, whose distorted wave is solved from the spherically averaged isotropic potential. The application to the water molecule shows reasonable agreement with the available experimental data.

Measurement of η meson production in γγ interactions and Γ(η → γγ) with the KLOE detector

Abstract We present a measurement of η meson production in photon-photon interactions produced by electron-positron beams colliding with $ \sqrt{s}=1 $ GeV. The measurement is done with the KLOE detector at the ϕ-factory DAΦNE with an integrated luminosity of 0.24 fb−1. The e + e − → e + e − η cross section is measured without detecting the out-going electron and positron, selecting the decays η → π + π − π 0 and η → π 0 π 0 π 0. The most relevant background is due to e + e − → ηγ when the monochromatic photon escapes detection. The cross section for this process is measured as σ(e + e − → ηγ) = (856 ± 8stat ± 16syst) pb. The combined result for the e + e − → e + e − η cross section is σ(e + e − → e + e − η) = (32.72 ± 1.27stat ± 0.70syst) pb. From this we derive the partial width Γ(η → γγ) = (520 ± 20stat ± 13syst) eV. This is in agreement with the world average and is the most precise measurement to date.

Molecular distorted-wave Born approximation for ionization of H2 by electron impact

The molecular distorted-wave Born approximation is proposed to study the (e, 2e) reaction for H2 targets. The wave functions of the incoming and outgoing electrons are obtained by solving the Lippmann–Schwinger equations, and the T-matrix in the Lippmann–Schwinger equations is calculated in a momentum space static-exchange-optical model. Triple differential cross sections are computed for incident energies of 100 and 250 eV in coplanar asymmetric geometry. Comparison of the present calculated results with the available experimental data in the literature reveals that there is good agreement.

Probing new physics models of neutrinoless double beta decay with SuperNEMO

The possibility to probe new physics scenarios of light Majorana neutrino exchange and right-handed currents at the planned next generation neutrinoless double beta decay experiment SuperNEMO is discussed. Its ability to study different isotopes and track the outgoing electrons provides the means to discriminate different underlying mechanisms for the neutrinoless double beta decay by measuring the decay half-life and the electron angular and energy distributions.

Cooling power of field emission from the n-type silicon semiconductor

The authors have theoretically investigated the cooling effect of field emission from n-type semiconductors. By considering the outgoing and incoming electrons in the region of emission, they make the numerical calculation of the energy exchange per field electron. It is found that even though the Joule heat is taken into account, the energy exchange is large enough for cooling the cathode. The cooling power sufficient for microelectronic device is obtained for field emission from the highly n-doped Si semiconductor.

Dynamical (e, 2e) studies of formic acid

We present triply differential cross sections for the electron impact ionization of the outer valence orbitals of formic acid (CHOOH) by 100 eV and 250 eV incident electrons. The experiments were performed under asymmetric kinematics, in which the outgoing ejected electron had an energy of 10 eV, over a range of momentum transfers. The experimental results are compared with theoretical calculations carried out using the sophisticated M3DW model, both with and without correlation-polarization-exchange terms included.

Minima in the triple differential cross sections for the electron-impact ionization of helium

We examine unusual minima found in the triple differential cross sections for the electron-impact ionization of helium for configurations where the incident electron is out-of-plane with respect to the plane in which the outgoing electrons are detected. The position of the experimentally determined minima are confirmed by time-dependent close-coupling calculations. An analysis is made of the origin of the minima in the cross section, where it is found they are due to deep destructive interference between the partial-wave amplitudes which contribute to the differential cross section.