Ejected Electrons Research Articles

Time-dependent rovibronic wave function of H2+ by multiconfiguration theory

Abstract We simulate the time-dependent rovibronic wave function of H 2 + in an intense, few-cycle 400 nm laser field using a time-dependent multiconfiguration method. By calculating the expectation value of the total angular momentum squared, the time-dependent expectation value of the internuclear distance, the induced dipole moment, and the probability of electron ejection, we show that rotational, vibrational and electronic excitation as well as ionization can be simulated. We compare the results obtained using the time-dependent multiconfiguration method with the results obtained using the standard two-state Born-Oppenheimer approximation and the close-coupling expansion. We find that the multiconfiguration results for a wave function constructed using 21 time-dependent orbitals are in good agreement with the close-coupling results, but that the two-state Born-Oppenheimer approximation leads to an underestimation of the induced dipole moment by a factor of two and an overestimation the expectation value of the total angular momentum squared by a factor of 2.3.

Nitrogen‐Nitrogen Bond Breaking in Irradiation Products of Hexanitrohexaazaisowurtzitane (CL‐20)

AbstractWhile the primary result of an interaction of ionizing radiation with an organic material is the ejection of electrons from molecular orbitals producing cations, the free electrons can further interact, yielding excited states; and, potentially, anions. In this work, we computed reaction barriers and energies for N−N bond breaking in the CL‐20 cation, anion, and excited state to investigate if CL‐20 degradation is accelerated after radiation exposure. We focused on N−N bond dissociation because it is the rate‐determining step in the thermal degradation of CL‐20. We found that N−N cleavage rapidly takes place in the CL‐20 cation and anion with greatly reduced reaction energies as compared to CL‐20. We also outlined a potential path for photodissociation of the N−N bond. While CL‐20 is kinetically stable, initial degradation occurs readily in its irradiation products. This is of importance for the performance of the explosive after high‐dose exposure and influences aging if CL‐20 is irradiated at a low dose over extended periods of time.

Novel Indolenine-Based hemicyanine dyes with extended π-Linker and auxiliary donor as potential Photosensitizers: Synthesis, Photophysical, electrochemical and computational Insights

Three novel hemicyanine dyes, D1-D3, were synthesized successfully based on dimethylaniline (DMA) and TPA donors and a carboxylated indolium vinyl acceptor linked through benzene unit as an extended π-spacer or through PTZ unit as an auxiliary donor to form the D1-π-A, D2-π-A & D2-D3-A systems, respectively. A multi-step process was conducted to yield the desired donor and acceptor intermediates. These were finally coupled through the Suzuki-Miyaura coupling and Knoevenagel condensation reactions to obtain the desired target dyes. A panchromatic response and a bathochromic shift of the ICT band maxima in the visible region were observed with the lowest band gap energy, Eg = 1.71 eV and λabs., max. = 590 nm, given by dye D3, were attributed to the presence of the auxiliary donor, PTZ. However, due to the high coplanarity of dye D1 it showed the highest absorptivity value of ε = 36462 M−1cm−1. The HOMO and LUMO levels are within the range suitable for smooth dye regeneration and electron ejection, EHOMO = -5.37 to −5.18 eV, and ELUMO = -3.47 to −3.27 eV. The density functional theory (DFT) and time-dependent TD-DFT at the B3LYP/6-31G(d,p) level were conducted to explore the bridged effect on geometric and TD-BHandH/6-31G(d,p) for optoelectronic properties.

Multiple differential electron spectra from detachment in collisions of 30–300-keV anions with atoms and molecules

We have measured triple differential momentum distributions for electron detachment in collisions of 30- and 300-keV anions (C− and Si−) with atoms and molecules (He, Ar, and N2). The entire angular range of the ejected electrons was covered. The binary encounter ring, well known from positive ion-atom collisions, was observed in most cases. In a quasifree-electron scattering model this structure represents elastic scattering of the active electron from the target. However, especially for the slowest projectiles, this model fails to reproduce the angular distributions. In this regime it is probably necessary to use quasimolecular models to describe the collision. Indications for a projectile cusp are observed, implying that excitation-induced dipole moments in the ion projectile may be important. Published by the American Physical Society 2024

Coherent control of multiphoton ionization of lithium atoms by a bichromatic laser field

We demonstrate a left-right asymmetry control of the photoelectron angular distribution in multiphoton ionization of Li atoms by a bichromatic laser field. By delaying the fundamental (780 nm) and its second harmonic relative to each other in steps of 130 attoseconds, we can vary the relative phase between the two laser fields with subwavelength accuracy and thereby steer the ejected electrons. Good agreement is found between the measurements and calculations at the appropriate intensities of the two harmonics. Published by the American Physical Society 2024

Identification of material by X-ray fluorescence analysis with a pyroelectric X-ray generator

By changing the temperature of Lithium Tantalate (LiTaO3) single crystal at moderate vacuum conditions leads to generation of strong electric field. The uncompensated polarization during the heating or cooling of the crystal causes the ejection of electrons from either the dielectric layer on the surface of the crystal or from a metal target depending on the polarity. The electrons are accelerated and gain energy of up to 100 keV. The energy of these electrons can be determined by measuring the end-point energy of the X-ray spectrum that resulted from the electron interactions with the target. The conception of a pyroelectric accelerator enabled us to develop compact (portable) electron source, which does not require an external high-voltage and the use of hazardous materials. The compact and portable nature of pyroelectric-driven particle sources holds significant promise for applications in materials science, particularly for materials analysis methodologies. The research demonstrates the feasibility of utilizing the X-ray signal generated by irradiation with electrons to identify elements in each sample. It is revealed that employing only the electron beam enables the successful acquisition of quantitative information regarding the sample structure through pyroelectric driven PD-PIXE analysis. These findings set the stage for the development of a compact and versatile apparatus for elemental analysis of materials based on a pyroelectric source.

Spectroscopy and dynamics of isolated anions: Versatile instrumentation for photodetachment and photoelectron spectroscopy.

Molecular anions are appealing targets for study because, compared with their neutral and cationic counterparts, they can be probed with conventional laboratory lasers without the need for multiphoton ionization schemes, and they provide spectroscopic details on the corresponding neutral molecules. Here, we describe a section of a modular instrument designed to perform high-throughput photoelectron and photodetachment spectroscopy of gas-phase anions, with future provision for time-resolved and isomer-selective spectroscopy. The instrument framework allows for the incorporation and adaptation of several ion sources, as demonstrated here with plasma (electric) discharge sources providing variable hard to soft ion generation conditions. The generated anions are separated according to their mass-to-charge ratio through time-of-flight mass spectrometry (m/zΔm/z = 500-600) and are focused into a set of perpendicular velocity-map imaging electrodes (ΔEE≈4%), where mass-selected anions are probed using laser light and the ejected electrons are velocity-map imaged. Instrument performance is demonstrated through the acquisition of photodetachment and photoelectron spectra for CH2CN-, showing sharp resonances in the vicinity of the detachment threshold assigned to rovibrational states of a dipole-bound anion and broader lifetime-limited spectral features at photon energies well above the threshold assigned to prompt autodetachment from a temporary anion resonance. Similar measurements could be performed on any molecular anions generated in the sources.

Catalysis of first triplet p-benzoquinone for electron ejection from sulfite: Significance of single electron transfer

In this study, the combination of p-benzoquinone (p-BQ) and sulfite under the ultraviolet (UV) irradiation demonstrated markedly superior efficiency in the ejection of hydrated electrons (eaq−) compared to the individual UV/p-BQ and UV/sulfite processes. Theoretical calculations reveal that the 1,2- and 1,4-addition of bisulfite (HSO3−) to p-BQ was unlikely to occur kinetically, and the 1,4-addition of sulfite (SO32−) might be the major pathway for the reaction with p-BQ. Via single electron transfer from the highest occupied molecular orbitals (HOMOs) of HSO3− and SO32− to the HOMO–1 of 3p-BQ*, the oxidation of HSO3− and SO32− by the first triplet state of p-BQ (3p-BQ*, the major excited species during the excitation) could result in the generation of HSO3•, SO3•− and semiquinone radical anion. This mechanism could elucidate the synergism of p-BQ and sulfite for ejecting eaq− in the water under the UV irradiation. Given the abundance of quinones in natural waters, these findings may be helpful for the utilization of sulfite to efficiently release eaq− in the water treatment applications.

Laser-assisted (e,2e) study with twisted electron beam on H-atom

We study the laser-assisted twisted electron beam impact ionization of the hydrogen atom in coplanar asymmetric geometry. We develop the theoretical model in the first Born approximation. In the presence of the laser field, we treat the incident and scattered electrons as Volkov waves; the ejected electron, moving in the combined field of the laser and residual ion H+ , as a Coulomb–Volkov wave function. In this communication, we compare the angular profile of triple differential cross-section (TDCS) for laser-assisted twisted electron beam incidence with the plane-wave, laser-assisted plane wave, and field-free twisted electron beam for (e,2e) processes for different orbital angular momentum (OAM) number (ml ) values. We analyze the effect of impact-parameter b of twisted electron beam and the laser parameters on the angular distribution of the TDCS. We study the (TDCS)av for the macroscopic target to examine the effect of opening angle θ p of the twisted electron beam on the angular profile of TDCS. We also observe the influence of coherent superposition of two Bessel states on the angular profile of TDCS. Our results clearly show the effects of laser parameters (electric field ɛ and number of photon exchanged (l)) and twisted electron beam parameters (OAM number (ml ) and opening angle (θ p )) on the angular distribution of TDCS.

Cross sections of cascade production of photoions after photoionization of the iodine atom in the 0.01–100 keV incident photon energy range

Ion yields upon the cascade decays of single vacancies in K to O shells of an isolated iodine atom are calculated by the method of construction and analysis of the cascade decay trees. Branching ratios needed for the simulations are calculated based on Pauli–Fock partial transition widths. Partial photoionization cross sections are calculated with accounting for the core relaxation effect and used to calculate the cross sections of I q+ photoions production in the 0.01–100 keV incident photon energy range. Accounting for the spin–orbit splitting and the splitting due to electron–electron interaction is shown to be important when calculating mean energies and probabilities of the transitions between energetically closely lying ionic configurations. On the other hand, inclusion of the additional shake-off electron ejections, in spite of complicating severely the decay trees, is found to affect little calculated cascade ions production probabilities.

The use of NADH anisotropy to investigate mitochondrial cristae alignment

Life may be expressed as the flow of electrons, protons, and other ions, resulting in large potential difference. It is also highly photo-sensitive, as a large proportion of the redox capable molecules it relies on are chromophoric. It is thus suggestive that a key organelle in eukaryotes, the mitochondrion, constantly adapt their morphology as part of the homeostatic process. Studying unstained in vivo nano-scale structure in live cells is technically very challenging. One option is to study a central electron carrier in metabolism, reduced nicotinamide adenine dinucleotide (NADH), which is fluorescent and mostly located within mitochondria. Using one and two-photon absorption (340–360 nm and 730 nm, respectively), fluorescence lifetime imaging and anisotropy spectroscopy of NADH in solution and in live cells, we show that mitochondria do indeed appear to be aligned and exhibit high anisotropy (asymmetric directionality). Aqueous solution of NADH showed an anisotropy of ~ 0.20 compared to fluorescein or coumarin of < 0.1 and 0.04 in water respectively and as expected for small organic molecules. The anisotropy of NADH also increased further to 0.30 in the presence of proteins and 0.42 in glycerol (restricted environment) following two-photon excitation, suggesting more ordered structures. Two-photon NADH fluorescence imaging of Michigan Cancer Foundation-7 (MCF7) also showed strong anisotropy of 0.25 to 0.45. NADH has a quantum yield of fluorescence of 2% compared to more than 40% for photoionisation (electron generation), when exposed to light at 360 nm and below. The consequence of such highly ordered and directional NADH patterns with respect to electron ejection upon ultra-violet (UV) excitation could be very informative—especially in relation to ascertaining the extent of quantum effects in biology, including electron and photonic cascade, communication and modulation of effects such as spin and tunnelling.

Real-time structural dynamics of the ultrafast solvation process around photo-excited aqueous halides.

This work investigates and describes the structural dynamics taking place following charge-transfer-to-solvent photo-abstraction of electrons from I- and Br- ions in aqueous solution following single- and 2-photon excitation at 202 nm and 400 nm, respectively. A Time-Resolved X-ray Solution Scattering (TR-XSS) approach with direct sensitivity to the structure of the surrounding solvent as the water molecules adopt a new equilibrium configuration following the electron-abstraction process is utilized to investigate the structural dynamics of solvent shell expansion and restructuring in real-time. The structural sensitivity of the scattering data enables a quantitative evaluation of competing models for the interaction between the nascent neutral species and surrounding water molecules. Taking the I0-O distance as the reaction coordinate, we find that the structural reorganization is delayed by 0.1 ps with respect to the photoexcitation and completes on a time scale of 0.5-1 ps. On longer time scales we determine from the evolution of the TR-XSS difference signal that I0: e- recombination takes place on two distinct time scales of ∼20 ps and 100 s of picoseconds. These dynamics are well captured by a simple model of diffusive evolution of the initial photo-abstracted electron population where the charge-transfer-to-solvent process gives rise to a broad distribution of electron ejection distances, a significant fraction of which are in the close vicinity of the nascent halogen atoms and recombine on short time scales.

A trajectory surface hopping study of the vibration-induced autodetachment dynamics of the 1-nitropropane anion

In this study, we investigate the autodetachment dynamics of the 1-nitropropane anion after vibrational excitation of the energetically lowest C–H stretching mode using our recently developed extended quantum classical surface hopping approach including the detachment continuum. Therein the detachment from an electronic bound anion state is treated as a nonadiabatic transition into discretized detachment continuum states for an ensemble of classical nuclear trajectories propagated on quantum mechanical potential energy surfaces. The initial ensemble is obtained by sampling a phase space distribution accounting for the vibrational excitation of the C–H stretching mode of the molecule to match the experimental conditions. The simulated kinetic energy distribution of the ejected electrons reproduces characteristic features of the available experimental data. Analysis of the nuclear dynamics points out that the approach to neutral-like geometries with decreased pyramidalization angle of the NO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} group and reduced the N–O bond lengths are the crucial factors enhancing the ultrafast autodetachment process in vibrationally excited 1-nitropropane. This is facilitated when the dipole-bound first excited state of the anion is populated, which is structurally similar to the neutral system. Although only a small transient population of this state is observed, it acts as an efficient doorway to the detachment continuum and is responsible for a significant amount of the ejected electrons.

Mathematical Modeling of Solar Systems

The photoelectric effect is the emission of electrons from metals under the action of light. In 1921, Einstein won the Nobel Prize for explaining the photoelectric effect, which says that light has nature of particulate or light extends in quanta called photons. More photons eject more electrons, but the energy of the ejected electrons can only increase if the photon's energy rises. The photovoltaic effect and photoelectric effect are not the same concept. These are two directly related terms but the difference is that the photoelectric effect releases electrons from the surface of the material, after exposure to a sufficient amount of energy from sunlight. The photovoltaic effect releases electrons pass between molecules of different material compounds, which causes an increase in voltage between the two electrodes. This discovery is the basis for the development of electricity generation from solar energy. Further development and achievement are given further in the work.

Directly imaging excited state-resolved transient structures of water induced by valence and inner-shell ionisation

Real-time imaging of transient structure of the electronic excited state is fundamentally critical to understand and control ultrafast molecular dynamics. The ejection of electrons from the inner-shell and valence level can lead to the population of different excited states, which trigger manifold ultrafast relaxation processes, however, the accurate imaging of such electronic state-dependent structural evolutions is still lacking. Here, by developing the laser-induced electron recollision-assisted Coulomb explosion imaging approach and molecular dynamics simulations, snapshots of the vibrational wave-packets of the excited (A) and ground states (X) of D2O+ are captured simultaneously with sub-10 picometre and few-femtosecond precision. We visualise that θDOD and ROD are significantly increased by around 50∘ and 10 pm, respectively, within approximately 8 fs after initial ionisation for the A state, and the ROD further extends 9 pm within 2 fs along the ground state of the dication in the present condition. Moreover, the ROD can stretch more than 50 pm within 5 fs along autoionisation state of dication. The accuracies of the results are limited by the simulations. These results provide comprehensive structural information for studying the fascinating molecular dynamics of water, and pave the way towards to make a movie of excited state-resolved ultrafast molecular dynamics and light-induced chemical reaction.

Dopant ionization and efficiency of ion and electron ejection from helium nanodroplets.

Photoionization spectroscopy and mass spectrometry of doped helium (He) nanodroplets rely on the ability to efficiently detect ions and/or electrons. Using a commercial quadrupole mass spectrometer and a photoelectron-photoion coincidence spectrometer, we systematically measure yields of ions and electrons created in pure and doped He nanodroplets in a wide size range and in two ionization regimes-direct ionization and secondary ionization after resonant photoexcitation of the droplets. For two different types of dopants (oxygen molecules, O2, and lithium atoms, Li), we infer the optimal droplet size to maximize the yield of ejected ions. When dopants are ionized by charge-transfer to photoionized He nanodroplets, the highest yield of O2 and Li ions is detected for a mean size of ∼5×104 He atoms per nanodroplet. When dopants are Penning ionized via photoexcitation of the He droplets, the highest yield of O2 and Li ions is detected for ∼103 and ∼105 He atoms per droplet, respectively. At optimum droplet sizes, the detection efficiency of dopant ions in proportion to the number of primary photoabsorption events is up to 20% for charge-transfer ionization of O2 and 2% for Li, whereas for Penning ionization it is 1% for O2 and 4% for Li. Our results are instrumental in determining optimal conditions for mass spectrometric studies and photoionization spectroscopy of molecules and complexes isolated in He nanodroplets.

Photogeneration of singlet oxygen catalyzed by hexafluoroisopropanol for selective degradation of dyes

Singlet oxygen (1O2) shows great potential for selective degradation of dyes in environmental remediation of wastewater. In this study, we showcased that 1O2 can be effectively generated from an anion complex composed of deprotonated hexafluoroisopropanol anion ([HFIP-H]‒) with hydroperoxyl radical (⋅HO2) via ultraviolet (UV) photodetachment. Electronic structure calculations and cryogenic negative ion photoelectron spectroscopy unveil critical proton transfer upon complex formation and electron ejection, effectively photoconverting prevalent triplet ground state 3O2 to long-lived excited 1O2, stabilized by nearby HFIP. Inspired by this spectroscopic study, a novel "photogeneration" strategy is proposed to produce 1O2 with the incorporation of atmospheric O2 and HFIP, acting as a catalyst. Conceptually, the designed catalytic cycle upon UV irradiation and electron injection is able to achieve different degradations of dye molecules in a controllable fashion from decolorization to complete mineralization, shedding new light on potential water purification.

Current driven red emission from graphene foam

The influence of DC current flow on graphene foam have demonstrated the broadband red emission centered at ∼750 nm, characterized by the threshold behavior and exponential increase of intensity with external applied current. The emission has taken a place from a whole large-area of graphene foam surface. Its mechanism was discussed in terms of current induced ionization of graphene responsible for the luminescent transition assisted by ejection of hot electrons.

Electron affinity measurement of hydrogen negative ion

Photodetachment Microscopy experiment was first carried out in the presence of an electric field by Blondel et al in 1996 for Bromine negative ion. It measures the spatial distribution of ejected electrons on the detector screen which is a direct view of the spatial structure of the wave function of an atomic electron in the form of a ring pattern. From a semi-classical point of view, this ring pattern is formed because of the interference between two electron waves; one is direct while the other is reflected from an electric field. Following Blondel's photodetachment microscopy experiment, a formula that displays the Newton Rings is derived using a theoretical imaging technique or hydrogen negative ion near a plane interface. The interface means an elastic plane in the vicinity of the source of photoelectrons. The direct and reflected electron waves in this formula generate quantum interference in the form of Newton Rings. It is found that the number of rings increases as we increase the photon energy of the laser light. This finding is in accordance with the very well-known Einstein photoelectric effect which finally provides help to find the electron affinity of the hydrogen negative ion very accurately.

Laser induced generation of hydrogen by using NdAlO3 nanocrystals as photocatalysts in alcohols

Laser Induced White Emission (LIWE) using focused infrared laser beam can emit hot electrons and, for this reason, has been described as capable of generating H2. NdAlO3 is described as a photocatalyst for H2 production in several alcohols using a focused 808 nm excitation; the process generated a low concentration of CH4 and no presence of carbon dots in the final solution, improving previous results using graphene foam. The proposed mechanism involves the ejection of hot electrons from the material and their subsequent absorption by the alcohol, ultimately leading to dehydrogenation. Besides that, relative permittivity was correlated with the amount of electrons emitted, which was demonstrated by a superb correlation between H2 production and relative permittivity of the media used. Higher relative permittivity media was able to emit more hot electrons, which ultimately produced more H2.