Ejected Electrons Research Articles

Electronic decoherence following photoionization: Full quantum-dynamical treatment of the influence of nuclear motion

Photoionization using attosecond pulses can lead to the formation of coherent superpositions of the electronic states of the parent ion. However, ultrafast electron ejection triggers not only electronic but also nuclear dynamics---leading to electronic decoherence, which is typically neglected on time scales up to tens of femtoseconds. We propose a full quantum-dynamical treatment of nuclear motion in an adiabatic framework, where nuclear wavepackets move on adiabatic potential energy surfaces expanded up to second order at the Franck-Condon point. We show that electronic decoherence is caused by the interplay of a large number of nuclear degrees of freedom and by the relative topology of the potential energy surfaces. Application to $\mathrm{H_2O}$, paraxylene, and phenylalanine shows that an initially coherent state evolves to an electronically mixed state within just a few femtoseconds. In these examples the fast vibrations involving hydrogen atoms do not affect electronic coherence at short times. Conversely, vibrational modes involving the whole molecular skeleton, which are slow in the ground electronic state, quickly destroy it upon photoionization.

Electron excited multiply charged argon ions studied by means of an energy resolved electron-ion coincidence technique

Multiply charged argon ions produced from decay of L-shell hole states by impact of a continuous beam of 3.5 keV electrons are studied for the first time using an energy resolved electron-ion coincidence technique. The TOF spectra of argon ions are measured in coincidence with 18-energy selected electrons emitted in a wide energy range (126–242 eV). The coincidence measurement between the energy selected electrons and the correlated ions specifies the individual decay channel for various multiply charged ions. New experimental data are obtained and reported on the correlation probability for production of argon ions with charge states 1+ to 4+ as a function of ejected electrons in the considered energy range. The relative correlation probability of producing different charge state ions and corresponding physical processes involved in their production are presented and discussed. It has been found that the maximum probability for production of Ar2+ ions correlated to ejected Auger electrons in the energy range of 205–209 eV is 100%. No theoretical predictions are available to compare with these results. The present study shows further that not only the auto-ionization and normal Auger transitions but also several other decay processes including Coster-Kronig transitions followed by Auger cascades with a fraction of shake process play important role in producing ions with charge states 1+ to 4+.

Dynamics of transfer ionization inp-He collisions at intermediate energies

We have performed a kinematically complete experiment for transfer ionization, i.e., the capture of one target electron by the projectile accompanied by the ejection of a second electron, for 50--100 keV $p$-He collisions by means of a reaction microscope. It was found that the electron momentum distribution projected onto the scattering plane is consistent with the prediction of an independent two-step mechanism involving a binary encounter. The deviation of the electron momentum distribution from the ideal binary ridge is attributed to binding energy effects and the interaction between the electron and the residual recoil ion. The good agreement between our measurements with the dynamic-screening classical trajectory Monte-Carlo calculations strongly suggests that electron-electron correlations play an important role in this two-electron process.

Differential cross sections for the single ionization of H2 by 75 keV proton impact

We have calculated the double and triple differential cross sections for electron ejection with energy of 14.6 eV in single ionization of H2 by 75 keV proton impact. A molecular version of the continuum distorted wave-eikonal initial state approach is applied, where the interaction between the projectile and the residual molecular ion is considered more properly than in previous applications of the method. For triple differential cross sections, the present results are in better agreement with the experimental data than those of other descriptions when large momentum transfer values are considered. For double differential cross sections the experimental data are reproduced quite well for both coherent and incoherent proton beams.

Asymmetric electron energy sharing in electron-impact double ionization of helium

We present the fully fivefold differential cross sections (FDCSs) for ($e,\phantom{\rule{0.16em}{0ex}}3e$) processes in helium within the first Born approximation. The calculation is performed for a coplanar geometry in which the incident electron is fast ($\ensuremath{\sim}6$ keV), the momentum transfer is small (0.24 a.u.), and for an asymmetric energy sharing between both slow ejected electrons at excess energy of 20 eV. Two cases have been considered: ${E}_{1}=15$ eV, ${E}_{2}=5$ eV and ${E}_{1}=8$ eV, ${E}_{2}=12$ eV. While waiting for new theoretical and experimental results for confrontations, in particular for asymmetric energy sharing, our results clearly demonstrate that, for the same incident energy, the same momentum transfer and the same excess energy, the ($e,\phantom{\rule{0.16em}{0ex}}3e$) process in helium with asymmetric energy sharing between ejected electrons is more likely than the case with symmetric energy sharing. The two- and three-dimensional representation of the FDCSs covering all possible values of the angle of ejections are presented and discussed. The theoretical cross sections are calculated by using a compact-kernel-integral-equation approach associated with the Jacobi matrix method to calculate a three-body wave function and which leads to a full convergence in terms of the basis size.

Internal Energy Loss of the Electrons Ejected in Neutrinoless Double Beta Decay

The excitations of the electron shell in neutrinoless double beta decay shifts the limiting energy available for ejected electrons. We present the general equations for this shift and make computations for the decays of two nuclei—germanium and xenon.

Visible and direct sunlight induced H2 production from water by plasmonic Ag-TiO2 nanorods hybrid interface

This report signifies the synthesis of TiO2 nanorods (TNR ~79nm) and nanospheres (TNS ~19nm) and their Ag loaded counterparts AgTNR and AgTNS for the photocatalytic hydrogen production from water under monochromatic visible and direct sunlight. The Ag-TNR nanohybrid junction was sensitized at a matching monochromatic wavelength of 457nm and sunlight to produce ~90 µmol and 105 µmol of gas, respectively, increase in the efficiency is explained due to the surface plasmon (SPR) effect of Ag nanoparticles and is also correlated to fluorescence quenching (due to better charge distribution along larger nano-interface), crystal structure and surface area (146m2g−1) of fabricated AgTNR nanocomposite. The elongated morphology of AgTNR led to the effective distribution of charge along larger interface resulting in the increase of photocurrent density (0.01mA/cm2) which boosts the reaction rate. Plasmonic metal (Ag) activated with matching wavelength to SPR produces an electric field and the TiO2 present in the proximity encounters these effects results in the formation of Schottky barrier, the SPR effect is also more towards Ag-TiO2 interface which results in the ejection of electron towards the conduction band of TNR.This study demonstrated that Ag nanoparticles loaded lengthy TiO2 nanorods (~79nm) exhibited highly improved H2 production (90 μmol) from water relative to TiO2 nanospheres (~19nm) due to the plasmonic effect at 457nm light irradiation that also exhibited better H2 production (105 μmol) rate under direct sun light (8h) exposure.

Photoprompted Hot Electrons from Bulk Cross-Linked Graphene Materials and Their Efficient Catalysis for Atmospheric Ammonia Synthesis.

Ammonia synthesis is the single most important chemical process in industry and has used the successful heterogeneous Haber-Bosch catalyst for over 100 years and requires processing under both high temperature (300-500 °C) and pressure (200-300 atm); thus, it has huge energy costs accounting for about 1-3% of human's energy consumption. Therefore, there has been a long and vigorous exploration to find a milder alternative process. Here, we demonstrate that by using an iron- and graphene-based catalyst, Fe@3DGraphene, hot (ejected) electrons from this composite catalyst induced by visible light in a wide range of wavelength up to red could efficiently facilitate the activation of N2 and generate ammonia with H2 directly at ambient pressure using light (including simulated sun light) illumination directly. No external voltage or electrochemical or any other agent is needed. The production rate increases with increasing light frequency under the same power and with increasing power under the same frequency. The mechanism is confirmed by the detection of the intermediate N2H4 and also with a measured apparent activation energy only ∼1/4 of the iron based Haber-Bosch catalyst. Combined with the morphology control using alumina as the structural promoter, the catalyst retains its activity in a 50 h test.

Angular distributions in the double ionization of DNA bases by electron impact

Ab initio calculations of the five-fold differential cross sections for electron-impact double ionization of thymine, cytosine, adenine and guanine are performed in the first Born approximation for an incident energy close to 5500 eV. The wavefunctions of the DNA bases are constructed using the multi-center wave functions from the Gaussian 03 program. These multi-center wave functions are converted into single-center expansions of Slater-type functions. For the final state, the two ejected electrons are described by two Coulomb wave functions. The electron–electron repulsion between the two ejected electrons is also taken into account. Mechanisms of the double ionization are discussed for each case and the best choices of the kinematical parameters are determined for next experiments.

Site-Selective Plasmonic Etching of Silver Nanocubes.

Plasmon-induced charge separation (PICS) at the interface between a plasmonic nanoparticle and semiconductor is now widely used for photovoltaics and photocatalysis. Here we take advantage of PICS for site-selective nanoetching of silver nanocubes on TiO2 beyond the diffraction limit. A silver nanocube exhibits two resonance modes localized at the top and bottom of the nanocube (distal and proximal modes, respectively) when it is placed on TiO2. We achieved selective etching at the top and the bottom of the nanocubes by PICS based on the distal and proximal modes, respectively. The site-selective nanophotonic etching reveals that the anodic reaction involved in PICS is induced by the plasmonic near field, which causes an external photoelectric effect. In particular, the distal mode etching at the top edges is explained in terms of ejection of energetic electrons (or hot electrons) from the distal site to TiO2 across the nanocube.

Relativistic effects in double ionization of helium via Compton scattering

In this article we present the relativistic calculations, based on the QED theory, for double ionization of helium by the Compton scattering. In particular, we calculate the contribution of the spin–flip amplitude to the total cross section. Due to this amplitude the final triplet spin state of the ejected electrons is possible. In the calculations based on the non–relativistic A2 term of the electron–photon interaction only the singlet spin state for the final electrons is allowed. We further assume the shake-off mechanism for process of double ionization. For the ground state of helium we use both the non–correlated and highly correlated wave function. We also discuss a degree of the scattered photon polarization in correlation with the formation of spin triplet state. Our calculations cover the photon impact energy range from 150 to 1000keV.

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.

Energy and angular analysis of ejected electrons (6–26 eV) from the autoionization regions of argon at incident electron energies 505 and 2018 eV*

High resolution ejected electron spectroscopy has been used to investigate a large number of Ar autoionizing states producing ejected electrons in the energy range from 6 to 26 eV at impact electron energies of 505 and 2018 eV and ejection angles of 40°, 90° and 130°. The full energy range has been divided into three regions which were analyzed separately. In the first one (6–9 eV) the obtained features are identified as the decay of the Ar2+(1D) at 45.11 eV. In the second one (9–14 eV) all features are identified as due to the decay of excited states formed by the excitation of 3s electrons to ns, np and nd subshells. The most prominent features are those arising from the excitation of 3s to nd(3,1D). In this series the 3s3p 63d(1D) state with FWHM of 0.040 eV is used as the calibration point for all measured spectra. In the third energy region (14–26 eV) a large number of features is observed. Most of them are identified as the decay of excited states of the type 3s3p 5 nl and 3s 23p 4 nl n′l′.

Role of the atomic electron shell in the doubleβdecay

We demonstrate that the limiting energy available for ejected electrons in the double-$\ensuremath{\beta}$ decay is diminished by about 400 eV due to inelastic processes in the atomic electronic shell.

COLLISIONLESS ELECTRON–ION SHOCKS IN RELATIVISTIC UNMAGNETIZED JET–AMBIENT INTERACTIONS: NON-THERMAL ELECTRON INJECTION BY DOUBLE LAYER

ABSTRACT The course of non-thermal electron ejection in relativistic unmagnetized electron–ion shocks is investigated by performing self-consistent particle-in-cell simulations. The shocks are excited through the injection of a relativistic jet into ambient plasma, leading to two distinct shocks (referred to as the trailing shock and leading shock) and a contact discontinuity. The Weibel-like instabilities heat the electrons up to approximately half of the ion kinetic energy. The double layers formed in the trailing and leading edges then accelerate the electrons up to the ion kinetic energy. The electron distribution function in the leading edge shows a clear, non-thermal power-law tail which contains ∼1% of electrons and ∼8% of the electron energy. Its power-law index is −2.6. The acceleration efficiency is ∼23% by number and ∼50% by energy, and the power-law index is −1.8 for the electron distribution function in the trailing edge. The effect of the dimensionality is examined by comparing the results of three-dimensional simulations with those of two-dimensional simulations. The comparison demonstrates that electron acceleration is more efficient in two dimensions.

Signal enhancement of neutral He emission lines by fast electron bombardment of laser-induced He plasma

A time-resolved spectroscopic study is performed on the enhancement signals of He gas plasma emission using nanosecond (ns) and picosecond (ps) lasers in an orthogonal configuration. The ns laser is used for the He gas plasma generation and the ps laser is employed for the ejection of fast electrons from a metal target, which serves to excite subsequently the He atoms in the plasma. The study is focused on the most dominant He I 587.6 nm and He I 667.8 nm emission lines suggested to be responsible for the He-assisted excitation (HAE) mechanism. The time-dependent intensity enhancements induced by the fast electrons generated with a series of delayed ps laser ablations are deduced from the intensity time profiles of both He emission lines. The results clearly lead to the conclusion that the metastable excited triplet He atoms are actually the species overwhelmingly produced during the recombination process in the ns laser-induced He gas plasma. These metastable He atoms are believed to serve as the major energy source for the delayed excitation of analyte atoms in ns laser-induced breakdown spectroscopy (LIBS) using He ambient gas.

Ionization of small molecules induced byH+, He+, andN+projectiles: Comparison of experiment with quantum and classical calculations

We report the energy and angular distribution of ejected electrons from $\mathrm{C}{\mathrm{H}}_{4}$ and ${\mathrm{H}}_{2}\mathrm{O}$ molecules impacted by 1 MeV ${\mathrm{H}}^{+}, \mathrm{H}{\mathrm{e}}^{+}$, and 650 keV ${\mathrm{N}}^{+}$ ions. Spectra were measured at different observation angles, from 2 to 2000 eV. The obtained absolute double-differential electron-emission cross sections (DDCSs) were compared with the results of classical trajectory Monte Carlo (CTMC) and continuum distorted wave, eikonal initial state (CDW-EIS) calculations. For the bare ${\mathrm{H}}^{+}$ projectile both theories show remarkable agreement with the experiment at all observed angles and energies. The CTMC results are in similarly good agreement with the DDCS spectra obtained for impact by dressed $\mathrm{H}{\mathrm{e}}^{+}$ and ${\mathrm{N}}^{+}$ ions, where screening effects and electron loss from the projectile gain importance. The CDW-EIS calculations slightly overestimate the electron loss for 1 MeV $\mathrm{H}{\mathrm{e}}^{+}$ impact, and overestimate both the target and projectile ionization at low emitted electron energies for 650 keV ${\mathrm{N}}^{+}$ impact. The contribution of multiple electron scattering by the projectile and target centers (Fermi shuttle) dominates the ${\mathrm{N}}^{+}$-impact spectra at higher electron energies, and it is well reproduced by the nonperturbative CTMC calculations. The contributions of different processes in medium-velocity collisions of dressed ions with molecules are determined.

Branching ratio and angular distribution of ejected electrons from Eu 4f76p1/2nd auto-ionizing states**Project supported by the National Natural Science Foundation of China (Grant No. 11174218).

The branching ratios of ions and the angular distributions of electrons ejected from the Eu 4f76p1/2nd auto-ionizing states are investigated with the velocity-map-imaging technique. To populate the above auto-ionizing states, the relevant bound Rydberg states have to be detected first. Two new bound Rydberg states are identified in the region between 41150 cm−1 and 44580 cm−1, from which auto-ionization spectra of the Eu 4f76p1/2nd states are observed with isolated core excitation method. With all preparations above, the branching ratios from the above auto-ionizing states to different final ionic states and the angular distributions of electrons ejected from these processes are measured systematically. Energy dependence of branching ratios and anisotropy parameters within the auto-ionization spectra are carefully analyzed, followed by a qualitative interpretation.

UV and ionizing radiations induced DNA damage, differences and similarities

Both UV and ionizing radiations damage DNA. Two main mechanisms, so-called direct and indirect pathways, are involved in the degradation of DNA induced by ionizing radiations. The direct effect of radiation corresponds to direct ionization of DNA (one electron ejection) whereas indirect effects are produced by reactive oxygen species generated through water radiolysis, including the highly reactive hydroxyl radicals, which damage DNA. UV (and visible) light damages DNA by again two distinct mechanisms. UVC and to a lesser extend UVB photons are directly absorbed by DNA bases, generating their excited states that are at the origin of the formation of pyrimidine dimers. UVA (and visible) light by interaction with endogenous or exogenous photosensitizers induce the formation of DNA damage through photosensitization reactions. The excited photosensitizer is able to induce either a one-electron oxidation of DNA (type I) or to produce singlet oxygen (type II) that reacts with DNA. In addition, through an energy transfer from the excited photosensitizer to DNA bases (sometime called type III mechanism) formation of pyrimidine dimers could be produced. Interestingly it has been shown recently that pyrimidine dimers are also produced by direct absorption of UVA light by DNA, even if absorption of DNA bases at these wavelengths is very low. It should be stressed that some excited photosensitizers (such as psoralens) could add directly to DNA bases to generate adducts. The review will described the differences and similarities in terms of damage formation (structure and mechanisms) between these two physical genotoxic agents.

Elaboration of modified electrodes through a direct anodic oxidation of chitin

By means of cyclic voltammetry study at platinum, gold and graphite electrodes, it is shown that the addition of chitin to a mixed solvent system acetonitrile/dimethylacetamide with the presence of LiCl, leads to the appearance of a quasi-reversible oxidation step and a subsequent generation of coated surfaces, indicating a direct electron ejection from this biopolymer. The electrochemical patterns of this redox system on platinum and Fourier transform infrared spectroscopic characterization of the electrodeposits, on Pt and Au, reveal a coupled chemical conversion of chitin, consecutively to the electrons transfer. By contrast, an adsorption phenomenon is expected on graphite disk. Besides, the electrogenerated films are oxidized with a biggest difficulty than chitin. The macroscale electrolysis of chitin at platinum grid leads to new insoluble oxidation products, which precipitate in the electrochemical cell and on the working electrode.