Mechanism Of Electron Capture Research Articles

Contribution of different electron-capture mechanisms in the fragmentation of CO23+ upon slow ion-molecule collision

Abstract We present recoil ion - projectile ion coincidence study on the three body fragmentation of CO23+ ion into C+ + O+ + O+ fragments upon impact with
Ar3+, Ar6+ and Ar8+ projectile ions having the same velocity of vp = 0.49 a.u. (atomic units) using recoil ion momentum imaging technique. The kinetic energy
release (KER) distributions are presented and effect of different electron-capture associated processes such as pure capture, electron capture followed by target ionization or projectile auto-ionization is discussed based on the analysis of KER corresponding to different final projectile charge state post collision. As the capture stabilization increased the relative yields in the KER distribution are found to decrease in the high KER side for low charged Ar3+ impact, while an increase is observed for Ar6+ and Ar8+ impacts. We discussed the interplay between electron-capture, projectile auto-ionization and target ionization for the dominance of particular process. We also observed a low-KER feature around 15 eV which was observed for electron
and proton impacts, which was not yet observed for highly charged ion impacts

Exploring Negative Chemical Ionization of Per- and Polyfluoroalkyl Substances via a Liquid Electron Ionization LC-MS Interface.

Per- and polyfluoroalkyl substances (PFASs) are a class of aliphatic manufactured compounds comprising fluoro-chemicals with varied functional groups and stable carbon-fluorine bonds. They are defined as "forever chemicals" due to their persistent and bioaccumulative character. These substances have been detected in various environmental samples, including water, air, soil, and human blood, posing significant health hazards. High-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS) is typically employed for the analysis of PFASs. Negative chemical ionization (NCI) is generally coupled to gas chromatography (GC) and offers high selectivity and sensitivity for compounds containing electronegative atoms, such as PFASs. The liquid electron ionization (LEI) interface is an efficient mechanism developed to robustly couple a liquid flow rate from an LC system to an EI or a CI source. This interface has been successfully utilized for pesticide determination in UHPLC-LEI-CI in negative ion mode (NCI). This work aims to evaluate different parameters involved in the ionization of PFASs analyzed in LC-LEI-NCI and subsequently develop a method for their detection in real samples. The parameters considered for this study include (i) a comparison of different CI reagent gases (methane, isobutane, and argon); (ii) the use of acetonitrile as both the chromatographic solvent and CI reagent gas; (iii) the presence of water and formic acid as chromatographic mobile phase components; and (iv) the mobile phase flow rate. The optimal combination of these parameters led to promising results. Tentative fragmentation pathways of PFASs in NCI mode are proposed based on the dissociative electron capture mechanism.

Understanding the electron capture mechanisms during heavy-ion collisions

Understanding the electron capture mechanisms during heavy-ion collisions

Feasibility study of nuclear excitation by electron capture using an electron beam ion trap

The nuclear excitation by electron capture (NEEC) mechanism is considered to be one of the most effective ways to excite nuclear isomers. Despite being proposed over 50 years ago, direct experimental evidence of NEEC is yet elusive. In this study, we propose an experimental scheme to examine the NEEC process using an electron beam ion trap (EBIT). In an EBIT, highly charged ions are bombarded by an electron beam, which can result in excitation of the nuclei in the trap through mechanisms such as NEEC and Coulomb excitation (CE), etc. Our calculations show that the total rates of NEEC production for some nuclei can reach over 0.1/s, which is higher than these from other mechanisms like CE. The proposed scheme may result in the confirmation of the existence of NEEC, and can also be used to study atomic nuclear excitation related processes.

Nearly isotropic Lyman-α 1 radiation following nonradiative electron capture in Xe54+ + Kr collisions at 197 MeV u−1

We measured the angular distribution of the subsequently emitted Lyman-α 1 transition of Xe53+* ions following nonradiative electron capture in collisions of 197 MeV u−1 Xe54+ projectiles with gaseous krypton target. The alignment of the projectile 2p 3/2 state and the relative population of its magnetic substates were further deduced. In contrast to the available lower energy results (Yang et al 2020 Phys. Rev. A 102 042803), it is found that at 197 MeV u−1 the Lyman-α 1 radiation becomes much less anisotropic and the magnetic substates are nearly statistically populated. Moreover, the experimental findings are compared with the results of the corresponding radiative electron capture mechanism, obviously different energy dependence of the magnetic-substate population is obtained and discussed using semiclassical arguments, which help reveal the population mechanism of excited states in collisions of highly charged high-Z ions with atoms.

High-energy two-electron transfer in ion-atom collisions

Two-electron transfer by fast heavy nuclei from heliumlike targets is studied. A detailed sequence of comprehensive computations is carried out in a large keV–MeV range of the projectile energies. This set is illustrated with total cross sections for double capture by alpha particles from helium atoms using several frequently applied four-body quantum-mechanical distorted wave models with the correct boundary conditions. The sensitivity of the obtained total cross sections is examined for different choices of the bound and continuum states. Especially at high energies, the influence of the compactness of the bound states is investigated by reference to the mechanism of the velocity matching kinematic double electron capture. Also considered is the dependence of these cross sections on the electronic screening of the projectile and the target nuclear charges in the bound and continuum states. The impact of this electronic shielding on total cross sections is assessed by reference to the corresponding bare nuclear charges in the bound and continuum states. Relative to all the available experimental data (100–6000 keV), the found striking model-dependence implies that two-electron transfer is sharply different from the associated one-electron transfer involving the same colliding particles.

Studies on the Processes of Electron Capture and Clustering of Benzyl Chloride by Ion Mobility Spectrometry.

This paper presents the results of the study on the course of the benzyl chloride (BzCl) ionization process in a drift tube ion mobility spectrometer (DT IMS) in which nitrogen was used as the carrier gas. BzCl ionization follows the dissociative electron capture mechanism. The chloride ions produced in this process take part in the formation of cluster ions. Using DT IMS allows for estimation of the value of the electron attachment rate for BzCl and the equilibrium constant for the cluster ion formation. The basic experimental method used in this work was to analyze drift time spectra obtained for the introduction of the sample to the spectrometer with the drift gas. The theoretical interpretation of the results is based on the mathematical description of the ion transport. This description takes into account the phenomenon of diffusion, as well as the processes of formation and dissociation of ionic clusters occurring during the movement of ions in the drift section.

Alignment of the projectile 2p3/2 state created by nonradiative electron capture in 95- and 146-MeV/u Xe54+ with Kr and Xe collisions

Anisotropic distributions of the Lyman-${\ensuremath{\alpha}}_{1}$ transition of the down-charged $\mathrm{X}{\mathrm{e}}^{53+*}$ ions are observed in fast $\mathrm{X}{\mathrm{e}}^{54+}$ with Kr and Xe collisions, in which the electron is transferred by the nonradiative electron capture mechanism. At the energy of 95 MeV/u, the alignment parameter of the projectile $2{p}_{3/2}$ state, ${\mathcal{A}}_{20}$, is determined to be \ensuremath{-}0.35 \ifmmode\pm\else\textpm\fi{} 0.02 for both targets. While the projectile energy is 146 MeV/u, the parameter for the Kr and Xe target is \ensuremath{-}0.28 \ifmmode\pm\else\textpm\fi{} 0.02 and \ensuremath{-}0.29 \ifmmode\pm\else\textpm\fi{} 0.04, respectively. The present results demonstrate that the electron capture to the ${m}_{j}=\ifmmode\pm\else\textpm\fi{}1/2$ magnetic substates is about two times more probable than to the ${m}_{j}=\ifmmode\pm\else\textpm\fi{}3/2$ ones.

Decomposition of Bis(acetylacetonate)zinc(II) by Slow Electrons.

The production of zinc-containing nanostructures has a large variety of applications. Using electron beam techniques to degrade organometallic molecules for that purpose is perhaps one of the most versatile methods. In this work, we investigate the scattering of low-energy (<12 eV) electrons with bis(acetylacetonate)zinc(II) molecules. We show that core excited and high-lying shape resonances are mainly responsible for the production of the precursor anions as well as the ligand negative fragments, which are observed exclusively at electron energies of >3 eV. The mechanisms for electron capture and then molecular dissociation are discussed in terms of density functional theory studies.

Analysis of Efficiencies of Electron Capture by Ions into Rydberg States and Inelastic n → n' Transitions in Plasma of Inert Gas Mixtures

A comparative analysis of efficiencies of the resonant and nonresonant mechanisms of electron capture by ions into Rydberg states of Xe(n) atoms and inelastic n → n' transitions between highly excited levels in the inert Rg/Xe gas mixture plasma that contains atomic (Xe+) and molecular (RgXe+ and Xe$$_{2}^{ + }$$) ions (Rg = Ne, Ar, and Kr, [Xe] $$ \ll $$ [Rg]) is carried out. The rate constants of resonant electron capture by Xe+ ions in triple collisions with Rg($$^{1}{{S}_{0}}$$) atoms of an inert gas and dissociative recombination of heteronuclear (RgXe+) and homonuclear (Xe$$_{2}^{ + }$$) ions are calculated based on our approach developed within the framework of the theory of nonadiabatic transitions between electron terms of the RgXe+ + e system. For the alternative mechanism of three-particle electron capture by Xe+ ions in collisions with Ne, Ar, and Kr atoms, the rate constants are calculated in the impulse approximation with account for the short-range and polarization electron–atom interactions. The rate constants of three-particle electron capture by ions and n → n' transitions in collisions with electrons are calculated using known theoretical models. Ranges of plasma ionization degrees, plasma electron and gas temperatures, and principle quantum number of Xe atom where resonant free–bound and bound–bound electron transitions play a key role are established.

Rydberg states population via three-body and dissociative recombination in low-temperature plasmas of rare gas mixtures

We study various physical mechanisms of electron-ion recombination accompanied by the formation of Rydberg atoms in plasmas containing atomic and molecular ions. Analytical approach to the description of resonant mechanism of ternary electron capture associated with the non-adiabatic energy transfer from free electron to the electronic shell of a quasimolecular ion is developed. Similar technique is used for the evaluation of the integral contribution of all rovibrational states of a bound molecular ion to the Boltzmann-averaged cross section and rate constant of dissociative recombination (DR). Simple expressions for cross sections and rate constants of non-resonant electron capture to Rydberg states in ternary electron-ion-atom collisions are derived in the impulse approximation. We perform a comparative analysis of the efficiencies of resonant and non-resonant three-body recombination of electrons with atomic ions and DR of molecular ions in plasmas of rare gas mixtures, Rg/Xe, with small relative concentration of xenon ([Xe] ≪ [Rg], Rg = He, Ne, Ar, Kr). It is shown that in a wide range of plasma parameters the resonant recombination mechanisms are predominant. The behavior and magnitudes of the recombination rate constants turn out to be quite different for heteronuclear ions with small (HeXe+ and NeXe+, D0 = 13.1 and 33 meV) and moderate (ArXe+ and KrXe+, D0 = 171 and 400 meV) values of the dissociation energy.

Анализ эффективностей процессов захвата электронов ионами в ридберговские состояния и неупругих переходов n n-=SUP=--=/SUP=- в плазме смесей инертных газов

We have carried out the comparative analysis of the efficiencies of resonant and non-resonant mechanisms of electron capture by ions into Rydberg states of atoms, Xe(n), and the inelastic n → n′ transitions between the highly-excited states in the plasmas of rare gas mixtures, Rg/Xe, containing atomic, Xe$^{+}$, and molecular, RgXe$^{+}$ and Xe$_{2}^{+}$, ions (Rg = Ne, Ar and Kr, [Xe]≪[Rg]). The rate constants of resonant electron capture by Xe$^{+}$ ions in ternary collisions with rare gas atoms, Rg($^{1}S_{0}$), and dissociative recombination of heteronuclear, RgXe$^{+}$, and homonuclear, Xe$_{2}^{+}$, ions were evaluated on the basis of the original approach within the framework of the theory of non-adiabatic transitions between electronic terms of RgXe$^{+}+e$ system. For the alternative mechanism of the three-body electron capture by Xe$^{+}$ ions in collisions with Ne, Ar and Kr atoms the calculations of the rate constants were carried out in the impulse approximation by taking into account both short-range and polarization electron-atom interactions. The rate constants of the three-body electron capture by ions and n → n′ transitions in collisions with electrons were calculated on the basis of the well-known theoretical models. We have determined the ranges of plasma ionization degree and electronic and gas temperatures as well as the principal quantum number of Xe atom which correspond to situations when the resonant free-bound and bound-bound transitions of electron play a key role.

Electron capture to the Rydberg atomic states in ternary collisions with neutral particles

SynopsisWe report on the results of theoretical comparative studies of different physical mechanisms of free electron capture to the Rydberg atomic states and bound-bound transitions in discharge plasmas of Ne/Xe and Ar/Xe mixtures containing atomic and molecular ions. Particular attention is paid to the role to the resonant non-adiabatic free-bound and bound-bound transitions due to collisions with neutral particles. We show that in a wide range of low-temperature plasma parameters the contribution of resonant processes to the population of low-lying Rydberg states is predominant.

Spin-orbit coupling effects on predicting defect properties with hybrid functionals: A case study in CdTe

Defect formation energies and transition levels are critical in determining doping behavior and recombination in semiconductor applications. Hybrid functionals are often used to overcome the band gap and delocalization errors of standard density-functional theory, and it is tempting to presume that the defect properties are correctly predicted once the hybrid functional mixing parameter reproduces the experimental band gap. However, pronounced spin-orbit coupling (SOC) effects can have an additional important role, which is clearly shown in this work by analyzing SOC effects originating from the $\mathrm{Te}\ensuremath{-}p$ orbitals in CdTe. In this work, we therefore use a hybrid functional that reproduces the experimental band gap when SOC is included, requiring a larger mixing parameter $\ensuremath{\alpha}=0.33$ compared to the conventional choice of $\ensuremath{\alpha}=0.25$. This hybrid functional was then used to predict defect properties, e.g., formation energy, transition level, and defect equilibrium. For defect states that do not directly involve the $\mathrm{Te}\ensuremath{-}p$ orbitals, such as the Cd interstitial (${\mathrm{Cd}}_{\mathrm{i}}$), we find that the effect of SOC on the defect levels can be captured by simply considering the SOC-induced band-edge shift. This is not the case for the A center ($\mathrm{C}{\mathrm{l}}_{\mathrm{Te}}\ensuremath{-}{V}_{\mathrm{Cd}}$ defect pair), where the localized acceptor state formed by $\mathrm{Te}\ensuremath{-}p$ orbitals is more directly affected by the SOC. For this defect, a mixing parameter as large as $\ensuremath{\alpha}=0.40$ is required to reproduce the experimental acceptor level. Regarding the implications for photovoltaics, we suggest that the ${\mathrm{Cd}}_{\mathrm{i}}$, which is the dominant compensating donor, could play an important role as a recombination center. While $\mathrm{C}{\mathrm{d}}_{\mathrm{i}}$ is usually thought of as a benign shallow donor, our predicted defect levels in the fully band-gap-corrected calculations are deep enough to raise a concern, and we propose a recombination mechanism for electron capture by $\mathrm{C}{\mathrm{d}}_{\mathrm{i}}$.

A precise analysis of the electron capture process through chirping wave frequency from a phase viewpoint

The mechanism of electron capture and acceleration in a chirped plane-wave laser pulse is investigated from the point of view of phase evolution and phase velocity synchronization. An in depth analysis shows that the phase evolution process, under appropriate conditions, changes at one special point due to the chirping effect, which causes the electrons to be captured in the pulse and remain in the acceleration stage for a long time rather than oscillating between acceleration and deceleration. This point is a turning point of the phase evolution, and the changing process of the phase direction is named U-turn.

Molecular characterization of naphthenic acids from heavy crude oils using MALDI FT-ICR mass spectrometry

Naphthenic acid (NA) fractions from heavy crude oils are typically analyzed in mass spectrometry via electrospray ionization (ESI). Here, we show that NA analysis is also possible by MALDI using a highly basic matrix (proton sponge). When compared with ESI, that allowed detection of six compound families, MALDI resulted in the observation of twenty-two compound families. Besides, MALDI analysis affords compositional-dependent information. Unlike ESI, where all NAs are detected as deprotonated molecules, in MALDI we observe both deprotonated molecules and radical anions. This indicates that ion formation in NA by MALDI can occur by either acid-base and electron-capture mechanisms, or both. Interestingly, the preferred ionization channel seems to be compound class dependent; for instance, the acid base mechanism (which allows detection of deprotonated NA species through a Brönsted-Lowry reaction) applies exclusively to NAs with high H/C ratios along the whole O/C range. On the other hand, for less saturated compounds both mechanisms apply, while the electron capture channel occurs exclusively in species with low H/C and high O/C ratios or high H/C and low O/C ratios (envelope of the van Krevelen plots). In summary, we demonstrate that MALDI(-) is an alternative method for the analysis of complex petrochemical samples offering additional advantages, when compared with ESI, such as increasing compositional space accessibility for polar samples, high throughput and exceptional tolerance to the presence of impurities and salts in the samples. Furthermore, exploration on semi-quantitative approaches in MALDI can provide additional advantages such as those offered by LC-ESI MS, currently used to quantify naphthenic acids.

Continuum distorted-wave method in the two-electron charge exchange theory

Introduction. In the case of collisions with multi-charged ions of atoms, more complex than the hydrogen atom, other than single-electron charge exchange and ionization, other processes may occur. These are, first of all, the processes of two-electron capture, capture with simultaneous ionization or ion excitation and others. We shall stop on the problems of the theoretical description of the processes of two-electron capture in the region of intermediate and high collision velocities of ions with atoms. Purpose . Research the interactions of multi-charged ions with atoms in the region of intermediate and high collision velocities using theoretical methods. Methods. To describe the double charge exchange processes in high-energy ion-atom collisions a four-part formalism of continuum distorted-wave method (CDW-method), based on the integral Dodd-Graider's equations, were developed. Results. We obtained a matrix element that describes the two-step (Thomas) mechanism of electron capture through a continuous spectrum from a target atom into bound states relative to the fast -particle. For the reaction amplitude, in the approximation of the mechanism of simultaneous capture of two electrons, a general expression that takes into account Coulomb effects in the initial and final states is found. Conclusion. The application of the general theory is illustrated by the example of a two-electron charge exchange reaction in collisions of helium atoms with -particles. The results of calculations of the cross sections are in good agreement with the experimental and theoretical data. An attractive side of the proposed formalism is the consistent consideration of the asymptotics of wave functions in both channels of the reaction, which takes into account the long-range nature of the Coulomb interactions.

Considerations about projectile and target X-rays induced during heavy ion bombardment

Abstract In this work we present some results concerning the X-rays emitted by heavy ions during target bombardment. In this case, Cl4+ and Cl5+ ions with energies from 4 MeV to 10 MeV were employed to irradiate vitreous carbon planchets. Moreover, total X-ray production cross sections of titanium X-rays induced by chlorine ions were obtained as well for the same energy range. Only inner shell transitions were considered in the present work. The titanium target consisted of a thin film deposited over vitreous carbon planchets. The results indicate that the projectile X-ray yields increase as a function of the bombarding energy for the present energy range. Effects due to projectile charge state appears to be of minor importance at these low ion velocities. It is shown that a simple exponential function can represent the continuum background of such complex spectra. The chlorine transition rates Kβ/Kα obtained from chlorine acting as a projectile interacting with a carbon target are about half the value when compared to the chlorine Kβ/Kα ratios obtained when a LiCl target is bombarded with C+ and C3+ ions with energies from 2 MeV to 6 MeV. As far as the total X-ray production cross sections of Ti induced by chlorine ions are concerned, the ECPSSR theory underestimates the Ti total X-rays production cross sections by several orders of magnitude. The role of electron capture and possible mechanisms responsible for these effects are discussed.

Carrier capture in InGaN/GaN quantum wells: Role of electron-electron scattering

The competition of electron-electron interband scattering (ee) and longitudinal optical phonon emission (e-ph) as electron capture mechanisms is theoretically investigated in III-nitride quantum wells. The non-trivial separation of their scattering probabilities is discussed, and compact expressions for capture time are obtained in the framework of the quantum many-body formalism. At the typical operating conditions of light emitting diodes (LEDs), the model predicts an increasing importance of ee scattering as a capture mechanism with increasing carrier density. Verifications against recent experiments are presented to support this finding and confirm the need for population-dependent capture time expressions including both ee and e-ph mechanisms for an accurate description of LED carrier dynamics and efficiency.

Temperature-dependent recombination velocity analysis on artificial small angle grain boundaries using electron beam induced current method

The details of the process of carrier recombination via the Shockley-Read-Hall (SRH) defect level, at the grain boundaries of multicrystalline silicon, were investigated. For this, the temperature-dependent recombination velocities, as determined by experiments, were analyzed by the application of an electron beam induced current method. For the model, the misorientation angles at the grain boundaries were defined using a multi-seed casting-growth method. The results of our experiments indicated different temperature behaviors at low and high temperatures. These can be explained by controlling the process anticipated by the SRH model, that is, the process whereby minority carriers (electrons) are captured at lower temperatures, followed by the reemission of the carriers before recombination with Arrhenius behavior at higher temperatures. The minority capture process appeared to conform to the power law T−α temperature behavior. Thus, there are two candidate electron capture mechanisms, namely, cascade phonon emission capture for shallow centers and excitonic-Auger capture for deep centers. The activation energy for the reemission of carriers was around 0.1 eV. These findings regarding the temperature dependence are essentially independent of the misorientation angles, suggesting a common defect level and recombination mechanism. The difference in the recombination velocities can be regarded as being derived from the difference in the density at the defect level.