Electron Attachment Research Articles

Thermal electron attachment to halogenated silanes in the gas phase.

Silane derivatives play a crucial role in industrial plasma processes for the fabrication of various electronic devices such as lighting devices, solar cells, and displays. Accurate quantitative data are essential for modeling technological plasmas. This study reports the rate coefficients (k) and activation energies (Ea) for thermal electron attachment to Si2Cl6, Si (CH3)3CHF2, and SiCl (CH3)2Si(CH3)3, which are key parameters for understanding the underlying processes in plasmas. The results obtained for other silane derivatives were also analyzed and discussed. The measurements were conducted using the pulsed Townsend technique. In this technique, electrons generated by a laser under an electric field travel to the anode, inducing a charge on it. In the presence of a scavenger gas, electrons are captured, leading to a decrease in the rate of charge increase over time. The kinetic parameters were deduced from the shape of the pulse. The G4 method was used to obtain bond dissociation energies (BDEs). This study determined the kinetic parameters for thermal electron attachment to Si2Cl6, Si (CH3)3CHF2, and SiCl (CH3)2Si(CH3)3 for the first time. The rate coefficients at 298 K were found to be 2.17 ±0.04 × 10-9cm3s-1, 2.01 ±0.09 × 10-12cm3s-1, and 8.05 ±0.07 × 10-12cm3s-1, respectively. The corresponding activation energies were determined to be 0.37 ±0.04 eV, 0.29 ±0.03 eV, and 0.21 ±0.01 eV for Si2Cl6, Si (CH3)3CHF2, and SiCl (CH3)2Si(CH3)3, respectively. The experiment was conducted over the temperature range of 298-378 K. The findings of this study provide significant new insights into fundamental parameters such as rate coefficients and activation energies for thermal electron capture by chlorinated and fluorinated silane derivatives. These data contribute to advancing our understanding of thermal electron interactions with chlorosilanes, which can be utilized for controlling important species in the plasmas of various modern technologies.

Dynamics of hydride anion and acetyloxyl radical production by electron attachment to acetic acid.

We investigate the dynamics and site-selectivity in the dissociation of transient anions formed upon attachment of low energy electrons to acetic acid by anion fragment momentum imaging experiments. The resonances at 6.7 and 7.7eV are confirmed to dissociate exclusively by the O-H bond, while a third resonance at 9.1eV dissociates primarily by both C-H break and O-H break. A fourth resonance near 10eV is found to dissociate by O-H break. For each resonance, the measured kinetic energy release indicates two-body dissociation produces a neutral radical in the ground electronic state, for all four resonances. The measured angular distributions are consistent with all four resonances having A' symmetry.

Low-energy (0-9 eV) electron interaction with gas phase 1,3-dichlorobenzene: an experimental and theoretical study

Abstract Dichlorobenzene used widely in industry for the synthesis of complex products, such as polymers. The processes using this compound require, as the initial step, the breakage of the C-Cl bond. In this work, we study the interaction of electrons with 1,3 dichlorobenzene molecules not only below 2 eV [M. Mahmoodi-Darian et al. J. Phys. Chem. A 113 11923-14929 (2001)] but also at higher energies, i.e., up to 10 eV. In this investigated energy range, the electron induces the cleavage of the C-Cl bond producing essentially a Cl- anion and the chlorobenzene radical via dissociative electron attachment. The experimental measurements are completed with quantum scattering treatments providing the resonant states and also the integral scattering cross sections. These outcomes may potentially contribute to elaborate synthesis strategies using electrons (i.e., cold plasma, surface plasmon resonance, …)

Exploring electronic resonances in pyridine: Insights from orbital stabilization techniques.

Electron attachment to pyridine results in electronic resonances, metastable states that can decay through electronic or nuclear degrees of freedom. This study uses orbital stabilization techniques combined with bound electronic structure methods, based on equation of motion coupled cluster or multi-reference methods, to calculate positions and widths of electronic resonances in pyridine that exist below 10eV. We report four 2B1 and four 2A2 resonances, including one 2B1 not previously reported experimentally and two 2A2 resonances not reported at all in the literature. The two lower energy resonances are one-particle shape resonances, while the remaining are mixed or primarily core-excited resonances. Multi-reference perturbation theory provides the best description of these resonances, especially when their character is mixed. We describe the character of these resonances qualitatively and calculate Dyson orbitals, which provide information about their decay channels.

Theoretical Study on the Dissociation Mechanism of Thiophene in the UV Photoabsorption, Ionization, and Electron Attachment Processes

ABSTRACTA computational study on the intricate mechanism of thiophene ring‐fragmentation (TRF) in the UV photodissociation, dissociative ionization, and dissociative electron attachment process has been performed. The complete fragmentation process is studied using high level G4 composite method for neutral, cationic, and anionic species by elucidating a detailed mechanism for various reaction channels. The study shows that for neutral thiophene, the major pathway is the migration of H atom and subsequent fragmentation through a transition state yielding acetylene (HC≡CH) and H2C=C=S. However, for the thiophene cation, the acetylene (HC≡CH)+H2C=C=S+ channel is a two‐step and barrier less process. The onset of CH3+HC=C=C=S channel has been observed in both the thiophene cation and anion which was absent in the neutral analogue. Similarly, the onset of H2S+HC≡C—C≡CH channel has been found to operate only in the thiophene cation. Others, such as HCS and HS elimination channels have been found in all the species showing similar dissociation mechanism. For the thiophene anion, the TRF process is very much similar to that of thiophene cation. However, the reaction enthalpies of the various elimination channels in the anionic species are lower as compared to that of cationic species. During the study, the ionization energies and electron affinities of various molecules/radicals produced during the fragmentation process of thiophene were also computed.

Production of Nitrogen Dioxide, NO2-, Anion from Dissociative Electron Attachment to Nitromethane below 1 eV and Its Temperature Dependence: Direct vs Dipole Bound Mediated Processes.

Reaction induced by slow electrons is implicated in a large field of research and applications. Below 3-4 eV, dissociative electron attachment efficiently fragments molecules via (1) shape resonance or (2) mediated by the formation of a dipole bound anion. While the temperature dependence of process 1 is well-known, that of 2 is not clearly established. Nitromethane is the prototypical molecule for which the electron attachment leads to the formation of both a dipole bound and a covalent anion. We provide here a comprehensive study of the fragmentation of nitromethane by <1 eV electron and the unusual temperature effects attributed principally to process 2.

Dosimetric saturation effect study and correction calculation method of ionization chamber at ultra-high dose rate (FLASH)

Backgroundand Purpose: FLASH radiotherapy has aroused strong interest among researchers, but how to monitor dose in real time and lack of generally accepted ion correction model are one of the challenges. This study is based on previous research work, the dosimetric verification of FLASH ionization chamber was performed using a 200 keV electron beam irradiation platform at an ultra-high dose rate. At the same time, the finite element program is written to analyze and calculate the ion correction factor. In addition, the results are compared with the calculation results of Boag model. MethodsIn this study, the pressure of the sensitive volume in the detector was adjusted to 16 mbar for the purpose of dosimetry of dose rates in excess of 100 Gy/s. In order to monitor the response of the detector, the beam frequency and pulse width were adjusted accordingly. However, due to the saturation effect of the ionization chamber, the processes of electron ion pair drift, attachment, recombination and diffusion in the sensitive volume were modelled on the basis of the relevant physical principles. Finally, the correction factor was calculated by the finite element analysis. ResultsThe experimental results demonstrate that the FLASH ionization chamber is capable of meeting the requirements of dose measurement and beam monitoring of the electron beam at ultra-high dose rates. Furthermore, the analytical model is able to more accurately describe the saturation effect and calculate the correction factor. ConclusionIn this paper, the method of reducing air pressure is employed for the purpose of monitoring the dose of ultra-high dose rate. Simultaneously, the finite element method was employed to analyze the physical process of electron–ion pairs within the chamber and to calculate the ion correction factor analytically. A comparison with the Boag model indicates that the proposed approach is effective. However, the results exhibit a certain degree of divergence from experimental outcomes. This discrepancy may be attributed to the influence of the input parameters, which require further calibration to enhance the accuracy and the robustness of the model.

High-resolution anionic velocity map imaging apparatus for dissociative electron attachment dynamics study.

Dissociative electron attachment (DEA) of a molecular target XY, e- + XY → XY- → X + Y-, is an important process in plasma, atmosphere, interstellar space, and ionizing radiation. DEA dynamics, i.e., the formation and fragmentation of an electron-molecule resonant complex, can be unveiled by measuring the product Y- with the velocity map imaging (VMI) technique. However, it is still challenging to achieve a high-resolution VMI measurement. Recently, we developed a high-resolution DEA apparatus that combined the VMI technique with a trochoidal electron monochromator. The energy spread (around 500meV) of thermally emitted incident electrons can be reduced remarkably, but the monochromatized electrons become diffuse again in energy when being pulsed with an electric pulse applied on the grid electrode because the electron beam must be pulsed in the VMI measurement. Now this long-standing technical contradiction is settled by introducing a parallel resistance-capacitor circuit to the electrode of an electron gun. A delay-line detector is used for the VMI measurement, which allows the three-dimensional velocity or momentum images of multiple anionic yields to be recorded efficiently. Our high-resolution VMI apparatus works at a pulse frequency of 5kHz and an energy spread of about 120-150meV, and its credible performances are exhibited by the measurements of the DEA processes of CO(a3Π) and NO2.

Investigation in improving the Cs-free negative hydrogen ion production with short-pulse low power in the afterglow of pulse-power-modulated plasma sources

Abstract Pulse plasma ion sources have been shown to be capable of achieving high negative hydrogen ion densities ( n H − ) or currents. The fast cooling of the electrons and reduction in the electron density (n e) provide favorable plasma conditions to improve the H− production, with a high density ratio of negative hydrogen ions to electrons during the pulse-off period. The purpose of this research is to further improve the performance of volume-produced H− ion sources based on the pulse power modulation. In this study, a time-modulated negative hydrogen plasma sustained by 10 kHz pulse power at the typical gas pressure of 0.3 Pa was numerically investigated using a global model. The model is compared with measurements obtained in a pulsed radio frequency ion source and shows a reasonable agreement. A steplike low-high power strategy in the active glow period and a short-pulse low power in part of the afterglow period are employed to mitigate overshoot of the electron temperature (T e) in the initial stage of the pulse period and to optimize H− production in the afterglow, respectively. The model predicts that a small-magnitude, short-duration low power operation in the afterglow increases n H − and decreases n e from the onset of the low power until the beginning of the next high power pulse, due to a modest temporary increase in the T e (less than 2 eV). It facilitates dissociative electron attachments and thus H− formation. The reduction in the n e indicates that positive ions lost to the walls cannot be compensated by weak ionization. H− production with a low number of co-extracted electrons can be optimized by adjusting the magnitude and duration of the low power in the afterglow.

What does it take to stabilize a naphthalene anion?

We investigate attachment of slow electrons (0-10eV) to naphthalene (Np) clusters in a crossed beam experiment. Supersonic expansions under different conditions using different buffer gases generate the clusters: in He, Ne, and low pressure Ar, neat (Np)N clusters are formed, while we also observe mixed clusters of naphthalene with rare-gas atoms in co-expansion with Ar above 0.5bar and with Kr. Negatively charged (Np)n- and Rgm(Np)n- (Rg = Ar, Kr) clusters are analyzed by mass spectrometry, and electron energy dependent ion yields are measured. We show that the smallest stable naphthalene complex with an excess electron, the dimer (Np)2- anion, cannot be formed in a binary collision of a free electron with (Np)2 dimer, nor with (Np)3 trimer. Evaporation of a weakly bound Ar atom(s) from a mixed ArM(Np)2 cluster following electron attachment leads to the dimer (Np)2- anion. Larger (Np)n-, n > 3, transient cluster anions decay via evaporation of an Np unit on a timescale of tens of microseconds. The self-scavenging process opens around 6eV, where a naphthalene unit is electronically excited by the incoming electron, which is slowed down and trapped. However, the transient negative ion is efficiently stabilized only in the mixed clusters, from which Ar atom(s) can be evaporated.

Metastable Evaporation of Molecules from Water Clusters.

We probe the stability of water clusters by means of their metastable decay probability extracted from two-dimensional reflectron time-of-flight mass spectra. Two different methods are used to ionize and potentially excite the clusters and trigger the evaporation: (i) attachment of electrons with near-zero energies, producing negatively charged clusters, and (ii) electron impact ionization, producing protonated (H2O)nH+ clusters. The electron attachment is a soft ionization and therefore provides information about the size distribution of the neutral clusters in the beam due to a very limited amount of post-ionization loss of water molecules. A dependence of metastable fractions on the conditions of neutral clusters production prior to the electron attachment is reported. For the cations, the higher energy electron impact ionization leads to a more extensive metastable loss of water molecules. The results are discussed in the light of neutral cluster excitation energy distributions and, for negative clusters, also in terms of binding energies. The experiments demonstrate clearly the role of the excess electron vs the excess proton in the two different charge states of the clusters around sizes N = 50-55, for which binding energies of the anions are derived from the data.

Triple Electron Attachments with a New Intermediate-Hamiltonian Fock-Space Coupled-Cluster Method.

The implementation of a new intermediate-Hamiltonian Fock-space coupled-cluster (IHFSCC) scheme for the (3,0) sector of the Fock space is reported. In this IHFSCC approach, the three-body contributions in the cluster operator S(3,0) corresponding to the (3,0) sector of the Fock space are considered, while S(1,0) and S(2,0) at the (1,0) and (2,0) level only include one- and two-body operators. By introducing a suitable partition of the wave operator, the intermediate Hamiltonian, which only depends on the two-body operator of S(1,0), is obtained. S(2,0) and S(3,0) are not required within this new IHFSCC scheme, and a large reference space can be possibly employed. The performance of this (3,0) IHFSCC method in calculating triple ionization potentials and excitation energies for atoms and cations with a ground p3 configuration as well as adiabatic excitation energies for some molecules is investigated. The effect of the number of active virtual orbitals and three different types of orbitals, i.e., reference orbitals, restricted open-shell Hartree-Fock orbitals (ROHF) of the target systems, and canonicalized ROHF orbitals, on IHFSCC results, is also studied. Our calculations indicate that reasonable results can be achieved with this (3,0) IHFSCC method when a minimal reference space is employed. Further increasing the number of active orbitals does not necessarily improve the results. In addition, the IHFSCC results using canonicalized ROHF orbitals generally agree well with reference values, and they are not very sensitive to the number of active orbitals compared with results using the reference orbitals. The new (3,0) IHFSCC method can be applied to open-shell systems with three unpaired electrons with reasonable accuracy at a relatively low computational cost.

Dissociative electron attachment and Ar+ reaction with chromium hexacarbonyl, 296-400 K.

Dissociative electron attachment rate constants have been measured for Cr(CO)6 under thermal conditions, 296-400K, yielding Cr(CO)5- product. At 296K, 2.92 ± 0.70cm3s-1 was measured and a small decrease with temperature was observed (2.72 ± 0.70cm3s-1 at 400K). We additionally determined the cation products of Ar+ reacting with Cr(CO)6.

Electron-driven processes in enantiomeric forms of glutamic acid initiated by low-energy resonance electron attachment.

Low-energy (0-14eV) resonance electron interaction and fragment species produced by dissociative electron attachment (DEA) for enantiomeric forms of glutamic acid (Glu) are studied under gas-phase conditions by means of DEA spectroscopy and density functional theory calculations. Contrary to a series of amino acids studied earlier employing the DEA technique, the most abundant species are not associated with the elimination of a hydrogen atom from the parent molecular negative ion. Besides this less intense closed-shell [Glu - H]- fragment, only two mass-selected negative ions, [Glu - 19]- and [Glu - 76]-, are detected within the same electron energy region, with the yield maximum observed at around 0.9eV. This value matches well the energy of vertical electron attachment into the lowest normally empty π* COOH molecular orbital of Glu located at 0.88eV according to the present B3LYP/6-31G(d) calculations. Although the detection of asymmetric DEA properties a priori is not accessible under the present experimental conditions, "chirality non-conservation" can be associated with some decay channels. Evidently, the measured spectra for the L- and D-forms are found to be identical, the results, nevertheless, being of interest for the forthcoming experiments utilizing spin-polarized electron beam as a chiral factor in the framework of conventional DEA technique.

Biological study with molecular mechanism of imidazothiazole based Schiff bases as anti-Alzheimer agent: Insight into the role of synthesis, molecular docking and ADMET analysis

The current study aims to develop synthetic route and biological evaluation regarding a series of fused imidazothiazole derived Schiff base hybrid derivatives (1–17), synthesized by treating imidazothiazole bearing ester with hydrazine. The first intermediate imidazothiazole bearing hydrazide upon treating with ammonium thiocyanate was cyclized in the presence of 1,2-dioxane and potassium carbonate to second intermediate fused imidazothiazole bearing 2-aminothiadiazole. This intermediate was then mixed substituted benzaldehyde to afford fused imidazothiazole derived Schiff base hybrid derivatives. The current study revealed that the synthesized derivatives were examined and found with high inhibition profile against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in-comparison with marketed drug donepezil (IC50=7.20 ± 0.10 and 7.80 ± 0.20 µM for AChE and BuChE). Among all the derivatives, analog 11 (IC50=2.10 ± 0.30 and 2.80 ± 0.20 µM) was the one having highest inhibitory profile against both enzymes due to attachment of highly active tri-fluoromethyl group and hence regarded as potent analog. Furthermore, analog 7, 8, 9, 12 and 14 were also studied to exhibit excellent activity due to the attachment of electron donating groups and were found modest in contrast with the standard marketed drug. Protein-ligand interactions were observed through in-silico docking studies and their drug likeness properties were studied through ADMET analysis.

Dissoziative Elektronenanlagerungsdynamik eines vielversprechenden Krebsmedikaments zeigt sein Potential als Radiosensitizer

Abstract2‐Bromo‐1‐(3,3‐dinitroazetidin‐1‐yl)ethan‐1‐on (RRx‐001) ist ein Chemotherapeutikum für sauerstoffarme Tumore und zeigte bereits Synergieeffekte in Kombination mit Strahlentherapie. Die Wechselwirkung des Moleküls mit niederenergetischen Sekundärelektronen, die in großer Zahl in der physikalisch‐chemischen Phase der Bestrahlung gebildet werden, könnten für diesen Synergieeffekt verantwortlich sein. Die vorliegende Studie konzentriert sich auf die ersten Schritte in der Wechselwirkung von RRx‐001 mit niederenergetischen Elektronen, in denen das temporäre negative Ion gebildet wird und rasch fragmentiert. Die Kombination von Resultaten zweier Versuchsaufbauten erlaubt es uns, den Zerfall des RRx‐001 Anions auf verschiedenen Zeitskalen zu entflechten. Die alleinige Anwesenheit des eingefangenen Elektrons führt zu einer raschen Abspaltung von NO2 und HNO2, während NO2− und Br− Anionen direkt beziehungsweise über andere Zwischenprodukte gebildet werden. Auf Basis quantenchemischer Rechnungen schlagen wir einen bidirektionalen Wechsel zwischen π*(NO2) und σ*(C−Br) Zuständen vor, welcher die experimentellen Spektren erklärt. Die beobachtete schnelle Dynamik lässt auch Schlussfolgerungen für die Chemie des Anions in der kondensierten Phase zu.

Electron Attachment to the Nucleobase Uracil in Diethylene Glycol: The Signature of a Doorway.

The cellular environment plays a significant role in low energy electron-mediated radiation damage to genetic materials. In this study, we have modeled the effect of the bulk medium on electron attachment to nucleobases in diethylene glycol (DEG) using uracil as a test case, in accordance with recent experimental work on the observation of dissociative quasi-free electron attachment to nucleoside via excited anion radical in solution (in DEG). Our EOM-CCSD-based quantum mechanical/molecular mechanical (QM/MM) simulations indicate that the electron scavenging by uracil in DEG is much slower than that observed in the aqueous medium due to its viscosity. This work also establishes that a doorway mechanism exists in uracil microsolvated and bulk solvated with DEG, with the dipole-bound state and solvent-bound state acting as doorway states, respectively.

Generation of seed electrons in guided ionization waves in He–O2 mixtures: The effect of negative ion cluster formation

The kinetics of electrons and negative ions was numerically studied under the conditions, which are typical for multi-pulsed guided ionization waves in He flows ejected into ambient air. It was shown that, in He with a small admixture of O2 or air, O2− ions formed due to three-body electron attachment in the discharge afterglow are rapidly converted to O4− cluster ions in pulse off time. We suggested that seed electrons are generated at the leading edge of a pulse in two steps, and these steps are dissociation of O4− ions to form O2− ions followed by electron detachment from the O2− ions. The rate of O4− dissociation was calculated in He–O2 mixtures for various reduced electric fields on the basis of a Monte Carlo simulation. This rate, as well as the rate of electron detachment from O2− ions calculated previously, was used to simulate seed electron generation in a high-voltage nanosecond pulse in He–O2 mixtures for different gas pressures. It was shown that the formation of O4− ions drastically hinders the generation of seed electrons in multi-pulsed guided ionization waves in He–O2 and He–air mixtures.

Revisiting a Chemical Route to the Formation of CN− in the Interstellar Medium

We discuss the HCN + H− reaction as a path to the formation of CN−, the smallest cyanopolyyne anion observed in several interstellar environments. We first obtain the new ab initio reactive potential energy surface using a full 5D representation, where only the C–N bond is kept fixed, and discuss the neural network procedure employed to yield an accurate fit for the dynamics. The reaction is then investigated by using a quasi-classical trajectory approach to scan the low-temperature range of the dark molecular clouds where the anion has been sighted. Calculations are extended to room temperature to make a successful comparison with existing experimental data. We further present reduced dimensionality modeling of the reaction as a 2D process within a variational-transition state treatment with the inclusion of long-range forces. The dominant role of such forces in producing large reaction rate coefficients is discussed for both treatments, which yield very similar sizes and behavior of such coefficients from 50 to 300 K. The implications of our results for the interstellar medium formation of the CN− species via this chemical route are discussed, suggesting its greater significance over the radiative electron attachment paths, whose rate coefficients were found by recent calculations to be orders of magnitude smaller.

Fourth-Order Algebraic Diagrammatic Construction for Electron Detachment and Attachment: The IP- and EA-ADC(4) Methods.

We present a non-Dyson fourth-order algebraic diagrammatic construction formulation of the electron propagator, featuring the distinct IP- and EA-ADC(4) schemes for the treatment of ionization and electron attachment processes. The algebraic expressions have been derived automatically using the intermediate state representation approach and implemented in the Q-Chem quantum-chemical program package. The performance of the novel methods is assessed with respect to high-level reference data for ionization potentials and electron affinities of closed- and open-shell systems. While only minor improvements over the corresponding third-order methods are observed for one-hole ionization and one-particle electron attachment processes from closed-shell systems (MAEIP-ADC(4) = 0.27 eV and MAEEA-ADC(4) = 0.05 eV), a significantly enhanced performance is found in case of open-shell reference states (MAEIP-ADC(4) = 0.11 eV and MAEEA-ADC(4) = 0.02 eV). A particularly appealing feature of the novel methods is their accurate treatment of satellite transitions. For closed-shell reference states, we obtain accuracies of MAEIP-ADC(4) = 0.81 eV and MAEEA-ADC(4) = 0.27 eV, while in case of open-shell reference states, mean absolute errors of MAEIP-ADC(4) = 0.15 eV and MAEEA-ADC(4) = 0.27 eV are found.