High-energy Ionization Research Articles

Signatures of X-Ray-dominated Chemistry in the Spectra of Exoplanetary Atmospheres

High-energy radiation from stars impacts planetary atmospheres, deeply affecting their chemistry and providing departures from chemical equilibrium. While the upper atmospheric layers are dominated by ionizations induced by extreme-ultraviolet radiation, deeper into the atmosphere, molecular abundances are controlled by a characteristic X-ray-dominated chemistry, mainly driven by an energetic secondary electron cascade. In this work, we aim at identifying molecular photochemically induced fingerprints in the transmission spectra of a giant planet atmosphere. We have developed a numerical code capable of synthesizing transmission spectra with arbitrary spectral resolution, exploiting updated infrared photoabsorption cross sections. Chemical mixing ratios are computed using a photochemical model tailored to investigate high-energy ionization processes. We find that in the case of high levels of stellar activity, synthetic spectra in both low and high resolutions show significant, potentially observable out-of-equilibrium signatures arising mainly from CO, CH4, C2H2, and HCN.

Design and Study of a Large-Scale Microwave Plasma Torch with Four Ports

The microwave plasma torch (MPT) has gained popularity in industrial applications due to its high energy density, ionization levels, and high temperature. However, the non-uniform and unstable plasma generated by microwave plasma sources has limited the production of large-scale MPTs. This paper proposes a novel MPT device utilizing a four-port microwave source (2.45 GHz, 4 kW) to address these issues. The improved plasma uniformity and stability are achieved through the new structure, and the microwave efficiency is enhanced by introducing the focusing dielectric in the coupled cavity. Using a 3D electromagnetic field model, microwave plasma model and fluid model, the paper optimizes the geometry and inlet mode of the MPT device. Experimental results show that the novel MPT device can generate a plasma torch with a maximum height of 545 mm, a working range of 10–95 L/min, and a microwave efficiency up to 86%. The proposed device not only competently meets industrial requirements, but also provides design ideas and methods for future MPT devices.

Exoplanet weather and climate regimes with clouds and thermal ionospheres

Context. Gaseous exoplanets are the targets that enable us to explore fundamentally our understanding of planetary physics and chemistry. With observational efforts moving from the discovery into the characterisation mode, systematic campaigns that cover large ranges of global stellar and planetary parameters will be needed to disentangle the diversity of exoplanets and their atmospheres that all are affected by their formation and evolutionary paths. Ideally, the spectral range includes the high-energy (ionisation) and the low-energy (phase-transitions) processes as they carry complementary information of the same object. Aims. We aim to uncover cloud formation trends and globally changing chemical regimes into which gas-giant exoplanets may fall due to the host star’s effect on the thermodynamic structure of their atmospheres. We aim to examine the emergence of an ionosphere as indicator for potentially asymmetric magnetic field effects on these atmospheres. We aim to provide input for exoplanet missions such as JWST, PLATO, and Ariel, as well as potential UV missions ARAGO, PolStar, or POLLUX on LUVOIR. Methods. Pre-calculated 3D GCMs for M, K, G, F host stars are the input for our kinetic cloud model for the formation of nucleation seeds, the growth to macroscopic cloud particles and their evaporation, gravitational settling, element conservation and gas chemistry. Results. Gaseous exoplanets fall broadly into three classes: i) cool planets with homogeneous cloud coverage, ii) intermediate temperature planets with asymmetric dayside cloud coverage, and iii) ultra-hot planets without clouds on the dayside. In class ii), the dayside cloud patterns are shaped by the wind flow and irradiation. Surface gravity and planetary rotation have little effect. For a given effective temperature, planets around K dwarfs are rotating faster compared to G dwarfs leading to larger cloud inhomogeneities in the fast rotating case. Extended atmosphere profiles suggest the formation of mineral haze in form of metal-oxide clusters (e.g. (TiO2)N). Conclusions. The dayside cloud coverage is the tell-tale sign for the different planetary regimes and their resulting weather and climate appearance. Class (i) is representative of planets with a very homogeneous cloud particle size and material compositions across the globe (e.g., HATS-6b, NGTS-1b), classes (ii, e.g., WASP-43b, HD 209458b) and (iii, e.g., WASP-121b, WP 0137b) have a large day-night divergence of the cloud properties. The C/O ratio is, hence, homogeneously affected in class (i), but asymmetrically in class (ii) and (iii). The atmospheres of class (i) and (ii) planets are little affected by thermal ionisation, but class (iii) planets exhibit a deep ionosphere on the dayside. Magnetic coupling will therefore affect different planets differently and will be more efficient on the more extended, cloud-free dayside. How the ionosphere connects atmospheric mass loss at the top of the atmosphere with deep atmospheric layers need to be investigated to coherently interpret high resolution observations of ultra-hot planets.

Investigation the fully differential cross section of helium atom single ionization by fast protons impact with three and four-body formalism

In the present work, the fully differential cross section of atomic helium ionization by protons impact at high energy ranges is calculated. The calculations of the fully differential cross section have been performed by using the three-body formalism in the first order Born-Faddeev approximation with an active electron model and four body formalism with the first Born approximation. In order to investigate the collision dynamics accurately, the first order Born-Faddeev approximation has been performed by using the single parameter and Hartree Fock as single-electron wave functions and in the first order Born approximation, the two-electron wave functions of Hylleraas and Silverman are used with considering the electron correlation. The fully differential cross sections at different ejected electron energies and momentum transfers are compared with the available experiment and theoretical results. The results show that the effects of electronic correlation are considerable at high impact energy range and ionization process.‎

Enhancement in non-linear optical properties of carbon nitride (C2N) by doping superalkali (Li3O): A DFT study

A systematized analysis of the electronic as well as the nonlinear optical properties of carbon nitride (C2N) doped with superalkali (Li3O) has been investigated through density functional theory (DFT) methods of B3LYP, LC-BLYP, and CAM-B3LYP at 6-31G (d,p) basis set. The FMOs value by the B3LYP method of DFT has been proved more promising to the experimental value of carbon nitride. So, it is employed as a more reliable method for computations. Doped molecules (M2 and M3) have a high interaction energy (-6.68 eV) and vertical ionization energy (3.46 eV), reduced energy gap in comparison with pure C2N indicating that designed complexes are more stable than pure C2N surface. The up-turn of UV absorption, dipole moment, and first hyperpolarizability have improved the electronic properties and interaction energies between the superalkali and carbon nitride after doping. The first hyperpolarizability and dipole moment of Li3O doped with pure surface has been increased up to 321,498 au and 5.31 D respectively. All results proved that Li3O doped with carbon nitride is a potential approach to synthesize the material by doping super alkali on carbon nitride for nonlinear optical devices.

Deuterium Adsorption on Free-Standing Graphene.

A suitable way to modify the electronic properties of graphene—while maintaining the exceptional properties associated with its two-dimensional (2D) nature—is its functionalisation. In particular, the incorporation of hydrogen isotopes in graphene is expected to modify its electronic properties leading to an energy gap opening, thereby rendering graphene promising for a widespread of applications. Hence, deuterium (D) adsorption on free-standing graphene was obtained by high-energy electron ionisation of D and ion irradiation of a nanoporous graphene (NPG) sample. This method allows one to reach nearly 50 at.% D upload in graphene, higher than that obtained by other deposition methods so far, towards low-defect and free-standing D-graphane. That evidence was deduced by X-ray photoelectron spectroscopy of the C 1s core level, showing clear evidence of the D-C sp bond, and Raman spectroscopy, pointing to remarkably clean and low-defect production of graphane. Moreover, ultraviolet photoelectron spectroscopy showed the opening of an energy gap in the valence band. Therefore, high-energy electron ionisation and ion irradiation is an outstanding method for obtaining low defect D-NPG with a high D upload, which is very promising for the fabrication of semiconducting graphane on large scale.

Forward-backward asymmetry in electron impact ionization of CO.

We experimentally investigate the molecular-orientation dependence of high-energy electron-impact ionization of CO. The direction of the molecular-axis with respect to the momentum transfer vector K is deduced from the angular correlation between the fragment ion and the scattered electron. The experimental results on the 3 2Π ionization reveal that at small momentum transfer, the ionization probability near the threshold is higher when K points toward the C atom along the molecular axis than when it is in the opposite direction. Such a forward-backward asymmetry does not appear in single-photon ionization and requires non-dipole contributions. It is also shown that the {4 2Σ+ + 5 2Σ+ + 6 2Σ+} ionization preferentially takes place in the vicinity of the molecular orientation parallel to K at small momentum transfer, while non-dipole contributions cause the decrease in the relative intensity of the parallel direction.

A novel investigation in the electronic broadening of spectral line profiles: Application to neutral magnesium in plasmas

We present in this work a new simple estimation of Stark broadening of neutral atoms in plasmas. This is achieved by exploiting the S-matrix unitarity criteria to get a more precise estimation of the minimum of the impact parameter. The latter depends on a critical velocity of the free electrons. The result is: the collision operator is the sum of two contributions; the first is from electrons velocities less than the critical velocity (slow electrons), and the second is from electrons with velocities greater than the critical velocity (fast electrons). When the reduced critical velocity is very small (vc≪1), it is shown that the strong collision contribution can be expressed by Meijer G-functions. This corresponds to high energy ionization element in stellar plasmas. Then we applied our theoretical results to a plasma consisting of magnesium. We find a good agreement with experimental and with others theoretical results for a range of electron densities and temperatures.

Electron Bessel States in High-Energy Ionization

The creation of electron Bessel states of large topological charge is discussed in the context of high-energy photoionization. We show that, for short (three cycle) driving pulses of circular polarization and intensities of 5 × 1016 Wcm−2, it is possible to obtain electron vortex states with orbital angular momentum of few thousands units of ℏ. Our analysis is based on the quasi-relativistic strong-field approximation where an additional term, the relativistic mass correction, is accounted for. The effect of this modification, together with the recoil corrections, over the energy spectra of photoelectrons is also analyzed.

Theoretical analyses for an alkali laser pumped by a pulsed light source

Diode-pumped alkali lasers (DPALs) have drawn much attention since they were proposed in 2001. Until now, most theoretical studies have related to the DPALs pumped by a continuous wave or a square-wave light source, but the theoretical reports for a DPAL pumped by a pulsed source still keep rare. In this study, the authors set up a kinetic model for a pulsed DPAL with the high energy transition and ionization processes taken into account. The spontaneous emission that coupled with the lasing mode is theoretically analyzed in the simulation. Additionally, the authors improve the algorithm to simulate the averaged laser intensity in time domain. Our theoretical results and experimental data in two published literatures coincide with each other and the correctness of our kinetic model can be demonstrated. The study should be useful for the design of an efficient pulse-pumped DPAL.

Constraining the stellar energetic particle flux in young solar-like stars

AbstractAnomalies in the abundance measurements of short lived radionuclides in meteorites indicate that the protosolar nebulae was irradiated by a large number of energetic particles (E≳ 10 MeV), often called solar cosmic rays. The particle flux of the contemporary Sun cannot explain these anomalies, but, similar to T Tauri stars, the young Sun was more active and probably produced enough high energy particles. However, the stellar particle (SP) flux of young stars is essentially unknown. We model the impact of high-energy ionization sources on the chemistry of the circumstellar environment (disks and envelopes). The model includes X-ray radiative transfer and makes use of particle transport models to calculate the individual molecular hydrogen ionization rates. We study the impact on the chemistry via the ionization tracers HCO+ and N2H+. We argue that spatially resolved observations of those molecules combined with detailed models allow for disentangling the contribution of the individual high-energy ionization sources and to put constraints on the SP flux in young stars.

Iodine Prophylaxis in the Case of Nuclear Accident.

On 26th April, 1986 the greatest accident of nuclear plant in Czernobyl occured and isotopes with high percentage of release were erupted: 33-Xe, 131-I, 132-Te, 134-Cs and 137-Cs. The radioactivity of the isotopes was very high - for instance: 33-Xe 6500 PBq, 131-I 1760 PBq. Rest of the 15 isotopes represented similar radioactivity with shorter percentage of release. The most exposed group of people were 237 liquidators, and 11600 people living around had to be evacuated when the limit dose for a person (5mSv) was crossed. Ionizing radiation on the molecular level produces high energy radicals, water radiolysis and ionization of the atoms leading to damage of the enzymes activity centers and receptors, cell membranes DNA, intracellular lysosomes, and especially important for ATP synthesis - mitochondria. These destructions lead to tissue and organs damage. The aim of this article is the presentation of the protective property of iodine application in the case of nuclear accident. In Poland at that time, effective iodine prophylaxis did not exist. In the face of such exposition, a special Governement Commission was appointed. When permissioned maximal dose for children and adolescents 50mSv appeared in some areas of the country, the Commission made a decision about obligatory administration of a single pharmacological dose of potassium iodide for all children and adolescents till age 16. No relevant recent patents were available for this WHO report. In this way, the dose of 131-I to thyroid for inhabitants in high, moderated, and low contaminated regions were reduced by about 45%. However, from 1987 to 1997 increase in prevalence of the differentiated thyroid cancer in adults in Polish population especially in women over 40 years old in the southern part of Poland was observed. Actually in European countries work 185 nuclear power plants and to 2045 another 100 is planned. In 1999, WHO issued recommendations on iodine prophylaxis in the case of nuclear accident.

Organic Salt Semiconductor with High Photoconductivity and Long Carrier Lifetime

AbstractIntrinsic photogeneration of charge carriers in organic semiconductors is generally attributed to high energy ionization or exciton dissociation by a strong electric field. Here, high bulk photoconductivity is reported in pristine pentamethine cyanine films with photocurrent onset at the band‐edge of the organic semiconductor. Single‐layer cyanine diodes with selective hole and electron contacts show linear dependence of photocurrent with reverse voltage and light intensity. Numerical drift‐diffusion simulations reveal that the linear resistor behavior stems from low and unbalanced carrier mobilities giving rise to negative space charge. Slow bimolecular recombination kinetics of photoinduced charges obtained by time delayed charge extraction measurements show strongly reduced Langevin recombination with long carrier lifetime of the order of a millisecond. Such reduced charge carrier recombination puts forward a materials concept to be exploited in photodiodes and more generally in optoelectronic devices.

Generation of attosecond electron beams in relativistic ionization by short laser pulses

Ionization by relativistically intense short laser pulses is studied in the framework of strong-field quantum electrodynamics. Distinctive patterns are found in the energy probability distributions of photoelectrons, which are sensitive to the properties of a driving laser field. It is demonstrated that these electrons are generated in the form of solitary attosecond wave packets. This is particularly important in light of various applications of attosecond electron beams such as in ultrafast electron diffraction and crystallography, or in time-resolved electron microscopy of physical, chemical, and biological processes. We also show that, for intense laser pulses, high-energy ionization takes place in narrow regions surrounding the momentum spiral, the exact form of which is determined by the shape of a driving pulse. The self-intersections of the spiral define the momenta for which the interference patterns in the energy distributions of photoelectrons are observed. Furthermore, these interference regions lead to the synthesis of single-electron wave packets characterized by coherent double-hump structures.

Ratios of double to single ionization of He and Ne by strong 400-nm laser pulses using the quantitative rescattering theory

We present numerical simulations of the ratio between double and single ionization of He and Ne by intense laser pulses at wavelengths of 390 and 400 nm, respectively. The yields of doubly charged ions due to nonsequential double ionization (NSDI) are obtained by employing the quantitative rescattering (QRS) model. In this model, the NSDI ionization probability is expressed as a product of the returning electron wave packet (RWP) and the total scattering cross sections for laser-free electron impact excitation and electron impact ionization of the parent ion. According to the QRS theory, the same RWP is also responsible for the emission of high-energy above-threshold ionization photoelectrons. To obtain absolute double-ionization yields, the RWP is generated by solving the time-dependent Schr\odinger equation (TDSE) within a one-electron model. The same TDSE results can also be taken to obtain single-ionization yields. By using the TDSE results to calibrate single ionization and the RWP obtained from the strong-field approximation, we further simplify the calculation such that the nonuniform laser intensity distribution in the focused laser beam can be accounted for. In addition, laser-free electron impact excitation and ionization cross sections are calculated using the state-of-the-art many-electron $R$-matrix theory. The simulation results for double-to-single-ionization ratios are found to compare well with experimental data and support the validity of the nonsequential double-ionization mechanism for the covered intensity region.

Control of relativistic ionization by polarization of short laser pulses

The Born approximation is applied to study the high-energy ionization that is driven by short, relativistically intense laser pulses. Assuming the fixed radiation flow through a surface of the laser focus, we investigate the optimal conditions for generating most energetic photoelectrons. We demonstrate that, under such constraint, one can control the photoelectron spectra using the polarization of the driving field. More precisely, the most energetic electrons are produced for a nearly linear polarization of the laser field. At the same time, the resulting electrons are detected in a narrow angular window which is of great importance for their potential applications; one of them being the generation of attosecond electron pulses.

High-energy ionization by relativistically intense laser pulses

High-energy ionization by relativistically intense, laser pulses is investigated within the relativistic strong-field approximation. It is shown that the momentum distribution of photoelectrons is focused around a spiral, the analytical form of which is derived from the saddle-point analysis of probability amplitudes. The geometry of this spiral allows one to clearly interpret the exact numerical results of the ionization probability distributions and to identify the photoelectron momentum domains in which the interference- and the interference-free patterns are observed. It is also demonstrated that attosecond single-electron wave packets can be created in this process. Thus, it opens new research opportunities for the four-dimensional electron diffraction experiments, which can be conducted in large-scale laser facilities such as ELI or XCELS.

Study of phase separation in an InGaN alloy by electron energy loss spectroscopy in an aberration corrected monochromated scanning transmission electron microscope

Abstract

Effect of rescattering potential on the high-energy above-threshold ionization of a model-H atom

The high-energy above-threshold ionization of a model-H atom (with 1s state and the same binding energy as H atom) in a few-cycle laser pulse is investigated by using the improved strong-field approximation (ISFA), where the spherical shell potential is used as the rescattering potential. The results obtained from numerically solving time-dependent Schrodinger equation(TDSE) are regarded as the benchmark results. Our results show that the energy distributions in high-energy region obtained from ISFA calculations using the spherical shell potential may either match or be better than those from ISFA using Yukawa potential and zero-range potential in the laser with wavelengths of 800 and 1200 nm. In addition, the influence of the rescattering potential on the density of probability at different ejection angles is also discussed in this paper.

Identification of Unsaturated and 2H Polyfluorocarboxylate Homologous Series and Their Detection in Environmental Samples and as Polymer Degradation Products.

A pair of homologous series of polyfluorinated degradation products have been identified, both having structures similar to perfluorocarboxylic acids but (i) having a H substitution for F on the α carbon for 2H polyfluorocarboxylic acids (2HPFCAs) and (ii) bearing a double bond between the α-β carbons for the unsaturated PFCAs (2uPFCAs). Obtaining an authentic sample containing 2uPFOA and 2HPFOA, we optimized a mass-spectrometric multiple-reaction-monitoring (MS/MS) technique and then identified uPFCA and HPFCA homologous series in sludge-applied agricultural soils and fodder grasses for cattle grazing. Analysis of samples from a degradation experiment of commercial fluorotelomer-based polymers (FTPs), the dominant product of the fluorotelomer industry, confirmed that commercial FTPs are a potential source of uPFCAs and HPFCAs to the environment. We further confirmed the identity of the uPFCAs by imposing high-energy ionization to decarboxylate the uPFCAs then focused on the fluorinated chains in the first MS quadrupole. We also employed this high-energy ionization to decarboxylate and analyze PFCAs by MS/MS (for the first time, to our knowledge). In exploratory efforts, we report the possible detection of unsaturated perfluorooctanesulfonate in environmental samples, having a conceptual double-bond structure analogous to uPFOA. Using microcosms spiked with fluorotelomer compounds, we found 2uPFOA and 2HPFOA to be generated from unsaturated 8:2 fluorotelomer acid (8:2 FTUCA) and propose β- and α-oxidation mechanisms for generation of these compounds from 8:2 FTUCA. In light of these experimental results, we also reexamined the proposed biodegradation pathways of 8:2 fluorotelomer alcohol.