Search

We present the angular distribution of the ejected electron for single ionization of He by fast proton impact. A four-body formalism of the three-Coulomb wave is applied to calculate the triple differential cross sections at several impact energies in the scattering, perpendicular and azimuthal planes. Moreover, the three-body formalism of three-Coulomb, two-Coulomb and first Born approximation models has also been used to study the many-body effect on electron emission and the validity of the models. In the three-Coulomb wave model, the final state wave function incorporates distortion due to the three-body mutual Coulombic interaction. In this formalism, we use an uncorrelated and correlated Born initial state, which consists of a plane wave for the incoming projectile times a two-electron bound state wavefunction of the helium atom representing the 1s2(1S) state. But, in the case of the three-body formalism, the initial state wavefunction consists of a long-range Coulomb distortion for the incoming projectile and one active electron of the He atom described by the Roothaan–Hartree–Fock wavefunction. The structure with a single or two peaks with unequal intensity is observed in the angular distributions of the triple differential cross sections for the different kinematic conditions. In addition, the influence of static electron correlations is investigated using different bound state wavefunctions for the ground state of the He target. In the four-body formalism, the present computations are very fast by reducing a nine-dimensional integral to a two-dimensional real integral. Despite the simplicity and speed of the proposed quadrature, the comparison shows that the obtained results are in reasonable agreement with the experiment and are compatible with those of other theories. [ABSTRACT FROM AUTHOR]

Modern gas chromatography-mass spectrometry (GC–MS) allows for the analysis of complex samples, such as fragrances. However, identifying all the constituents in natural fragrance mixtures, especially allergens that need to be listed on product labels, is a significant challenge. This is primarily due to the high complexity of the sample and the fact that electron ionization, the most commonly used ionization method in GC–MS, produces numerous nonspecific fragment ions, often resulting in the absence or very low abundance of the molecular ion. These factors affect confidence in assigning the analyte. In this study, we demonstrate that the combination of GC × GC separation, with high mass resolution and accurate mass measurements, as well as chemical ionization in addition to traditional electron ionization, becomes an efficient tool for reliable qualitative analysis of a mixture containing 100 fragrance allergens, even when many of them are closely related species or isomers. The proposed approach expands the applicability of the comprehensive GC × GC-HRMS method, which includes complementary ionization techniques, from studies on anthropogenic priority pollutants and emerging contaminants to the analysis of natural products. Although targeted qualitative and quantitative analysis of allergens in the modern laboratories is well organized, GC × GC-HRMS, being a useful complement to routine quality control of volatile allergens in fragrances, definitely gives an additional contribution to the analytical cases when conventional 1D-GC–MS faces some problems or uncertainties. [ABSTRACT FROM AUTHOR]

Here we present measurements of dissociative and non-dissociative cross-sections for the electron impact of the CF4 molecule. The present experiments are based on a Recoil Ion Momentum Spectrometer (RIMS), a standard gas mixing setup for CF4, and a reference gas. The measurements were carried out at several electron energies up to 1 keV, covering the energy range of previous experiments. We apply the relative flow technique (RFT) to convert the relative cross-sections measured by the RIMS into absolute values. Using the combination of RIMS and RFT, ion collection and calibration errors were minimized. The results were compared with theoretical and experimental studies available in the literature. Previous electron impact experiments present relative cross-sections or use correction terms for the absolute cross-sections due to losses of energetic ions. We elucidate the differences between the new measurement method and the existing ones in the literature and explain why the present method can be considered reliable. Furthermore, we show how reducing correction terms affects the results. [ABSTRACT FROM AUTHOR]

The sensitivity and accuracy of identifying volatile organic compounds using mass spectrometric gas analyzers operation in the electron ionization mode can be enhanced by increasing the number of ions formed in the ion source by varying the energy of ionizing electrons. The paper presents a comparison of data obtained by electron impact ionization at electron energy (EE) in the range of 25–105 eV for a number of organic substances belonging to different classes of organic compounds. an analysis using similarity matrices based on various similarity metrics was performed to interpret the dynamics of changes in the intensities of fragment ion peaks, and the influence of EE on the formation probability of the main fragment species of the substances under study and, accordingly, on the resemblance of a recorded mass spectrum to the reference mass spectrum from the database was shown. [ABSTRACT FROM AUTHOR]

Characterization of the inner-shell decay processes in molecules containing heavy elements is key to understanding x-ray damage of molecules and materials and for medical applications with Auger-electron-emitting radionuclides. The 1s hole states of heavy atoms can be produced by absorption of tunable x rays and the resulting vacancy decays characterized by recording emitted photons, electrons, and ions. The 1s hole states in heavy elements have large x-ray fluorescence yields that transfer the hole to intermediate electron shells that then decay by sequential Auger-electron transitions that increase the ion's charge state until the final state is reached. In molecules, the charge is spread across the atomic sites, resulting in dissociation to energetic atomic ions. We have used x-ray/ion coincidence spectroscopy to measure charge states and energies of Iq+ and Brq′+ atomic ions following 1s ionization at the I and Br K-edges of IBr. We present the charge states and kinetic energies of the two correlated fragment ions associated with core-excited states produced during the various steps of the cascades. To understand the dynamics leading to the ion data, we develop a computational model that combines Monte-Carlo/Molecular-Dynamics (MC/MD) simulations with a classical over-the-barrier model to track inner-shell cascades and redistribution of electrons in valence orbitals and nuclear motion of fragments. [ABSTRACT FROM AUTHOR]

We present new experimental and theoretical cross sections for electron-impact single ionization of Xe 12 + and Xe 13 + ions, and double ionization of Xe 12 + , Xe 13 + and Xe 14 + ions for collision energies from the respective ionization thresholds up to 3500 eV. The calculations use the fully relativistic subconfiguration-averaged distorted-wave approach and, partly, the more detailed level-to-level distorted wave method. We find that, unlike in previous work, our theoretical cross sections agree with our experimental ones within the experimental uncertainties, except for the near-threshold double-ionization cross sections. We attribute this remaining discrepancy to the neglect of direct-double ionization in the present theoretical treatment. Experimental and theoretical cross sections for electron-impact single ionization of Xe 12 + . [ABSTRACT FROM AUTHOR]

Electron ionization (EI) mass spectra of bi- and poly-ring carbo- and heterocycles including saturated and unsaturated spiranes, condensed ring and bridged ring systems are examined. Three, four, five, six-membered and larger rings are considered. The rings may include oxygen, sulfur, nitrogen, selenium or phosphorus atom or multiple hetero atoms. Characteristic fragmentation modes and diagnostically important ions generated by these compounds under EI are established. Detailed analysis of mass spectra of halides, alcohols and mercaptans, ethers and thioethers, aldehydes, ketones and thiones, carboxylic and thiocarboxylic acids, amines, amides and thioamides, nitro compounds, nitrites and nitrates of mono- and poly-ring carbo- and heterocyclic systems is performed. Basic fragmentation rules typical for a specific ring and general dissociation modes governed by a particular functional group are determined. The potential and its limitations of EI mass spectrometry in structure determination of unknowns are emphasized. [ABSTRACT FROM AUTHOR]

We report here an R-matrix study of electron collision with the BeO + molecular ion in its X 2 Π ground state and at a single bond length, namely its equilibrium R e = 2.7023   a 0 . Firstly, a good quality configuration interaction calculation is performed for the BeO + ground and excited states. We then perform scattering calculations using the R-matrix method to yield the cross-section for electronic excitation to several of its excited states. The electron impact dissociation of BeO + through the two lowest dissociation channels, namely the Be + (2 S g) + O (3 P g) and Be + (2 S g) + O (1 D g) dissociation channels, is estimated using the electronic excitation cross-sections. Rotational excitation cross-sections are provided for the j (= 0) → j ′ (= 1 , 2 , 3) rotational transitions. Our calculations also yield e + BeO + neutral Feshbach resonances and their widths which we present systematically categorized by their symmetry and quantum defects, and BeO-bound Rydberg states at the BeO + equilibrium. The full potential energy curves for the resonant states, their widths and the bound Rydberg states, whose details we propose to give in a subsequent work, can be the starting point of other collision calculations. [ABSTRACT FROM AUTHOR]

Electron ionization (EI) and molecular ion-generating techniques like chemical ionization (CI) are complementary ionization methods in gas chromatography (GC)-mass spectrometry (MS). However, manual curation effort and expert knowledge are required to correctly assign molecular ions to fragment spectra. MSdeCIpher is a software tool that enables the combination of two separate datasets from fragment-rich spectra, like EI-spectra, and soft ionization spectra containing molecular ion candidates. Using high-resolution GC-MS data, it identifies and assigns molecular ions based on retention time matching, user-defined adduct/neutral loss criteria, and sum formula matching. To our knowledge, no other freely available or vendor tool is currently capable of combining fragment-rich and soft ionization datasets in this manner. The tool's performance was evaluated on three test datasets. When molecular ions are present, MSdeCIpher consistently ranks the correct molecular ion for each fragment spectrum in one of the top positions, with average ranks of 1.5, 1, and 1.2 in the three datasets, respectively. MSdeCIpher effectively reduces candidate molecular ions for each fragment spectrum and thus enables the usage of compound identification tools that require molecular masses as input. It paves the way towards rapid annotations in untargeted analysis with high-resolution GC-MS. [ABSTRACT FROM AUTHOR]

The limit of detection of gas chromatography–electron ionization mass spectrometry (in scanning in the full ion current mode) is 10–11 to 10–10 g, depending on the substance. A full electron ionization mass spectrum of a substance can be recorded for 10–10 to 10–9 g, while the peak of the molecular ion in these mass spectra is often either absent or of low intensity. The minimum amount of a substance that can be detected by gas chromatography–atmospheric pressure photoionization mass spectrometry is 10–12 to 10–10 g and by gas chromatography–atmospheric pressure photochemical ionization mass spectrometry is 10–14 to 10–12 g, depending on the analyte and the reagent substance. For the amount of substance in the range from 10–9 to 10–10 g and up to the limit of detection, a mass spectrum consisting of the peaks of the M+ or MH+ ion or both of them is recorded. It gives selective information about the molecular weight of the analyte throughout the studied range. Identifying trace amounts of unknown components in complex mixtures can be achieved by sharing data from the mass spectra of electron ionization and atmospheric pressure photoionization. [ABSTRACT FROM AUTHOR]

This article discusses the synthesis and analysis of dialkyl esters of 5-norbornene-2,3-dicarboxylic acid, which are used in the creation of macromolecules. The researchers studied the fragmentation patterns of these esters using electron ionization mass spectra. The results showed that the synthesized esters are not highly resistant to electron ionization, resulting in the formation of various ions through different fragmentation pathways. This information is valuable for identifying and characterizing these compounds. The article also compares the mass spectra of isomeric endo,endo- or exo,exo-dialkyl ethers, finding that they are qualitatively identical with minor quantitative differences. However, the relative intensity of ion peaks associated with the elimination of alkyl substituents is lower for exo,exo-derivatives. This information can be used to confirm the spatial structure of the studied monomers. The study was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan, and the authors have no conflicts of interest. [Extracted from the article]

Using three different synthetic methods, 48 monoalkyl esters of 6 aliphatic dicarboxylic acids and 8 aliphatic alcohols were synthesized. Despite the method of synthesis, monoalkyl alkanedioates occurred in reaction mixtures along with corresponding dialkyl esters. This was caused both by a reaction mechanism and by possible secondary bimolecular disproportionation in solutions. However, for example, unlike monoalkyl phthalates, monoalkyl esters of aliphatic dicarboxylic acids appeared to be stable during their gas chromatographic separation. In no cases, characteristic chromatographic profiles indicating the decomposition of analytes in the chromatographic column were observed. The simultaneous presence of mono- and dialkyl esters in the samples allowed us to use the correlation of retention indices of mono- and dialkyl esters for their identification because the latter were characterized in more detail, namely, with RI(monoester) = aRI(diester) + b and some similar relations. The chromatographic peaks of monoalkyl alkanedioates (like for all carboxylic acids) on columns with nonpolar stationary phases were highly asymmetric. Their electron ionization mass spectra naturally indicated the presence of no signals of molecular ions. Mass spectra of monomethyl and monoethyl esters differed markedly from those of corresponding dialkyl esters, but they were similar for alcohols with R ≥ C3H7. [ABSTRACT FROM AUTHOR]

Electron-impact single ionization from levels of the ground configuration of the N+ ion is presented. Study analyses direct and indirect processes of the ionization. Convergence of the excitation-autoionization cross-sections is ensured by taking excitations up to shells with the principal quantum numbers n ≤ 10. The potential of the ionizing ion is used in the study. The scaled distorted wave cross-sections show a fairly good agreement with measurements. The study shows a presence of metastable states in the ion beams of experiments. [ABSTRACT FROM AUTHOR]

The single electron capture process from adenine molecules by H+, 3He+, N+, O+, and Ne+ ions with an energy of 6.3 keV has been studied. It was found that when one electron is captured by He+ and Ne+ ions, the dissociative capture process is dominant, which is fundamentally different from the processes of capture by singly charged ions of atoms with a lower ionization potential and multiply charged ions, as well as from the process of electron impact ionization. This effect is qualitatively explained within the framework of a quasimolecular model. [ABSTRACT FROM AUTHOR]

Here, we describe our pulsed helium droplet apparatus for spectroscopy of molecular ions. Our approach involves the doping of the droplets of about 10 nm in diameter with precursor molecules, such as ethylene, followed by electron impact ionization. Droplets containing ions are irradiated by the pulsed infrared laser beam. Vibrational excitation of the embedded cations leads to the evaporation of the helium atoms in the droplets and the release of the free ions, which are detected by the quadrupole mass spectrometer. In this work, we upgraded the experimental setup by introducing an octupole RF collision cell downstream from the electron impact ionizer. The implementation of the RF ion guide increases the transmission efficiency of the ions. Filling the collision cell with additional He gas leads to a decrease in the droplet size, enhancing sensitivity to the laser excitation. We show that the spectroscopic signal depends linearly on the laser pulse energy, and the number of ions generated per laser pulse is about 100 times greater than in our previous experiments. These improvements facilitate faster and more reproducible measurements of the spectra, yielding a handy laboratory technique for the spectroscopic study of diverse molecular ions and ionic clusters at low temperature (0.4 K) in He droplets. [ABSTRACT FROM AUTHOR]

Cross sections and thermal rate coefficients are computed for electron-impact dissociative recombination and vibrational excitation/de-excitation of the N 2 + molecular ion in its lowest six vibrational levels, for collision energies/temperatures up to 2.3 eV/5000 K. [ABSTRACT FROM AUTHOR]

Electron-impact ionization was analyzed for all 34 levels of the ground configuration of the Fe2+ ion. Both direct and indirect ionization processes are included in the study. For the direct process, the potential of the ionized ion was used to explain experimental data. For the indirect process, electron-impact excitation with subsequent autoionization was considered. The convergence of the cross sections of the indirect process was determined by considering the excitations up to shells with the principal quantum number n ⩽ 20. The main contribution to the indirect process was determined by the 3p → 3d excitations. The scaled distorted-wave approximation was applied to explain measurements for the Fe2+ ion. Scaling of the cross sections lowers values by ~35% at the peak for the ground level and ~50% for the highest level of the ground configuration of the Fe2+ ion. The experimental value for the single ionization threshold was used to provide better agreement with the measurements for the cross sections. This led to the cross sections for the levels of the ground configuration diminishing in size by 15–25%. The direct process contributes ~70% and ~50% to the total ionization from the lowest and highest levels of the ion, respectively. [ABSTRACT FROM AUTHOR]

The behavior of a series of previously unknown N-(5-aminothiophen-2-yl)- and N-[2-(methyl-sulfanyl)-1,3-thiazol-5-yl]isothioureas under electron impact ionization (70 eV) has been studied for the first time. 2-Thienylisothioureas give rise to a fairly stable molecular ion (Irel 11–25%), whereas no molecular ion peak is present in the mass spectra of 1,3-thiazolylisothioureas. A common fragmentation pathway of the molecular ions of 2-thienyl- and 1,3-thiazolylisothioureas involves cleavage of the C–N bond in the isothiourea fragment with charge localization on the imino nitrogen atom to give [R3SC≡NR2]+ ion (Irel 34–100%); furthermore, [M – R3SC=NR2]+ ion with charge localization on the amino nitrogen atom is formed from thienyl derivatives and is the most abundant (Irel 91–100%). The mass spectra of 1,3-thiazolylisothioureas also showed [M – MeSCN]+· and [MeSCS]+ ion peaks resulting from decomposition of the thiazole ring in the molecular ion. In addition, unlike 2-thienylisothioureas, the molecular ions of 1,3-thiazolyl analogs underwent Chet–N bond cleavage with charge localization on the thiazole fragment. [ABSTRACT FROM AUTHOR]

Gas chromatography–mass spectrometry (GC–MS) with Cold EI is based on interfacing GC and MS with supersonic molecular beams (SMBs) along with electron ionization of vibrationally cold sample compounds in SMB in a fly‐through ion source (hence the name Cold EI). Cold EI improves all the central performance aspects of GC–MS, and in this paper, we focus on its improvement of signal‐to‐noise ratio (S/N) and limits of detection (LODs). We found that the harder the compound for analysis with standard EI, the greater the Cold EI gain in S/N and LOD. The lower LOD and higher S/N of Cold EI emerge from a few reasons: (a) similar ionization yield as standard EI, (b) enhanced abundance of molecular ions, (c) elimination of vacuum background noise, (d) elimination of ion source‐related peak tailing and degradation, (e) ability to lower the elution temperatures via the use of high column flow rates, and (f) greater range of thermally labile and low‐volatility compounds that can be analyzed. We demonstrate the superior S/N and lower LOD of Cold EI versus standard EI in a range of compounds, from the simple‐to‐analyze octafluoronaphthalene all the way to reserpine and an organo‐metallic compound that cannot be analyzed by standard EI. These compounds include methyl stearate, cholesterol, n‐C32H66, large polycyclic aromatic hydrocarbons, dioctyl phthalates, diundecyl phthalate, pentachlorophenol, benzidine, lambda‐cyhalothrin, and methidathion. The significantly lower Cold EI LODs that can be over 1000 times better than in standard EI further result in far superior response linearity and greater measurement dynamic range. [ABSTRACT FROM AUTHOR]

We estimate the impact of asymmetry measurements of Deeply Virtual Compton Scattering (DVCS) with transversely polarized proton beam taken at a future Electron Ion Collider in China (EicC) on the extraction of Compton Form Factors (CFFs). The CFFs extracted from an analysis based on artificial neural-network approach are reweighted by means of pseudo-data generated in the expected kinematic region of EicC. We find a remarkable improvement in the extraction of CFF I m E , especially at the range of parton momentum fraction x ∼ 0.01, thus hinting for a future experimental probe of the parton orbital angular momentum. This work casts a glance at a practical implementation of Bayesian reweighting method on CFFs' impact study. [ABSTRACT FROM AUTHOR]

The electron ionization mass spectra of previously unknown N-(5-aminothiophen-2-yl)thioureas obtained in one preparative step from propargylamines and isothiocyanates were studied for the first time, and the main fragmentation patterns of these compounds were revealed. All the thienylthioureas studied form a molecular ion (Irel 7–61%), whose common fragmentation pathway {except for N-[5-(diethylamino)thiophen-2-yl]-N,N'-diphenylthiourea} is the cleavage of the R1N–C(=S) bond to form an intense [M – R2NHCS]+ ion peak (Irel 35–85%). The main fragmentation pathway of the molecular ions of N-[5-(diethylamino)thiophen-2-yl]-N,N'-diphenylthiourea is associated with the opening of the thiophene ring by the C2–S and C4–C5 bonds. N-[5-(Pyrrolidin-1-yl)thiophen-2-yl]- and N-[5-(piperidin-1-yl)thiophen-2-yl]thioureas characteristically undergo intense specific rearrangements that reveal themselves in the occurrence of unexpected primary fragmentation pathways of the molecular ions, the main of which is the elimination of an N,N'-dimethylcarbodiimide molecule. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The electron ionization mass spectra of substituted (β-hydroxy)sulfides, -sulfones, and their corresponding acetates of the 1,3-dioxepane series have been studied. The main regularities in the pathways of fragmentation of their molecular ions have been revealed. It has been shown that during electron ionization, the main directions of decomposition of the considered compounds are due to the elimination of substituents in the 1,3-dioxepane ring. In the case of 6-phenylthio-1,3-dioxepanes and 6-phenylsulfonyl-1,3-dioxepanes, the formation of ions associated with the breaking of C–S bonds with charge localization on the sulfur-containing fragment has been observed. [ABSTRACT FROM AUTHOR]

L-shell electron-impact ionization (EII) cross sections for highly charged tungsten ions were measured at incident electron energies of 29.10 and 38.92 keV using the Shanghai-EBIT. Resolved x-rays from radiative recombination (RR) processes were recorded with a high-purity Ge detector in a static electron energy scanning mode. Absolute EII cross sections were obtained by normalizing to the theoretical RR cross sections. The experimental results were compared with the calculated results using the relativistic distorted-wave method implemented in the flexible atomic code and the relativistic Lotz semi-empirical equation. The measurements showed general agreement with the calculated results by two theoretical methods for Li- to N-like W ions. The experimental uncertainties are not sufficiently small to discern the two theoretical results. Furthermore, the influence of Breit interaction on the EII cross sections of open L-shell tungsten ions was studied, and the effect is small but non-negligible. The measured EII cross sections of open L-shell tungsten ions would contribute to fusion plasma studies. [ABSTRACT FROM AUTHOR]

We report an experimental and theoretical investigation on the absolute ionization and fragmentation cross sections of tetrahydrofuran (THF, C4H8O), a base molecule of the DNA-backbone. The measurements enabled the identification of 50 ionic species produced by 12 eV up to 2000 eV electron impact which allowed us to make a close inspection of the mechanisms of both the primary vacancy production and the postcollisional fragmentation pathways which lead to the fragment ions. The experimental cross sections of the ionic species were examined in the framework of the fragmentation matrix model to attribute from which molecular orbitals (MOs) the electron is removed and find out the relative contribution of up to 15 outer and inner valence MOs in the fragment-ion production. A comparison between measured and calculated dissociative cross sections relative to the molecular parent ion cross section allowed us to clearly identify the prevalence of the single or double ionization in the fragment-ion production. Due to these different production mechanisms, the relative proportion of some ejected fragment-ions strongly depends on the impact energy. The single ionization of the MOs leading to selected fragment ions was compared to those measured at a low electron-impact energy using a reaction microscope with good agreement between the two techniques. The formation of the dications C4HnO2+, excluding the molecular parent dication, is also presented. [ABSTRACT FROM AUTHOR]

Electron impact ionization, also referred to as (e, 2e), involves the collision of an incident electron with a target (either an atom or an ion or a molecule), leading to the ionization of the target [[23]]. In recent years, the electron impact ionization of atoms, molecules and ions which are the most fundamental atomic processes has been studied using different theoretical and experimental techniques. Electron collision physics covers a broad range of processes in atoms and molecules. [Extracted from the article]

Previously unknown methyl N-(3-substituted thiophen-2-yl)carbamimidothioates were synthesized in one preparative step from hetero-substituted allenes (methoxy-, 1-ethoxyethoxy-, and 1H-pyrrol-1-ylallenes) and aliphatic, cycloaliphatic, and aromatic isothiocyanates, and their behavior under electron impact (70 eV) and chemical ionization (reactant gas methane) was studied for the first time. Unstable molecular ion derived from the title compounds under electron impact decomposes mainly via C–N bond cleavage in the carbamimido-thioate fragment with charge localization on the imide nitrogen atom. A similar fragmentation pathway is observed in the chemical ionization mass spectra of these compounds. Characteristic but low-intense ion peaks in the electron impact mass spectra of methyl N-(3-methoxythiophen-2-yl)carbamimidothioates become predominating in their chemical ionization mass spectra. The base peak in the chemical ionization mass spectra of methyl N-[3-(1H-pyrrol-1-yl)thiophen-2-yl]carbamimidothioates is that of the [M – SMe]+ ion. The most abundant ion in the chemical ionization mass spectrum of methyl N-[3-(1-ethoxyethoxy)thiophen-2-yl]-carbamimidothioate was generated by successive elimination of ethoxyethene and methanethiol molecules from the [M + H]+ ion. [ABSTRACT FROM AUTHOR]

Argon is being considered as an injected impurity to mitigate damage to divertors of DEMO caused by excessive heat flux. For a comprehensive understanding of Ar plasma, carefully evaluated atomic data are required. In this study, the electron-impact ionization cross-sections and rate coefficients for all atomic ions in the argon isonuclear sequence are calculated using the level-to-level distorted wave approximation. The calculated cross-sections and rate coefficients are compared with experimental data and other theoretical calculations. The calculated values are consistent with results reported in the literature, with differences not exceeding 20%. We fit the calculated cross-sections using an empirical formula. Additionally, we combine our ionization rate coefficients with the dielectronic- and radiative-recombination rate coefficients from other studies to determine the ionization balance. The obtained data are expected to be useful for plasma modelling involving argon impurities. [ABSTRACT FROM AUTHOR]

Laser desorption mass spectrometry was employed to study rubrene using three different sample preparation methods. Pressed-pellet and films drop-cast from solution were investigated with a laser-desorption time-of-flight spectrometer. Jet-cooled rubrene cations were produced in a supersonic molecular beam by laser desorption from a film-coated metal rod and detected with time-of-flight mass spectrometry. The films for this process were produced by vacuum sublimation of powder samples. The mass spectra from each of these samples contained the parent molecular ion and fragments resulting from phenyl ring elimination - a pattern similar to that produced by electron impact ionization. The amount of fragmentation varied with sample preparation and desorption laser wavelength. The rubrene cation was mass selected and studied with UV laser photodissociation at 355 nm. The resulting fragmentation mass spectrum indicated the loss of one or two phenyl groups, but no more than this. Computational studies of the ion energetics were used to investigate the stable fragment ion structures and understand the energetics of the dissociation process. [Display omitted] • Laser desorption mass spectrometry studied for rubrene at 532 and 355 nm. • Strong wavelength dependence for LD-ToF. • Photodissociation of mass-selected rubrene cation at 355 nm. • Computational studies of fragmentation energetics. • Elimination of biphenyl as dominant photochemical path. [ABSTRACT FROM AUTHOR]

Equilibrium charge-state fractions F q and average charges 〈 q 〉 are calculated for ion beams of superheavy Fl q + , Mc q + , Lv q + and Ts q + ions with charges q = 0 – 11 colliding with He atoms at ion energies E = 0.25 – 300 keV/u. The data are obtained using electron-loss and capture cross sections, calculated for He-gas pressures P = 0 and P = 0. 8 mbar with account for the target-density effect. At energies E ≈ 0.25 – 10 keV/u, the influence of the effect is found small, but at higher energies E ≥ 10 keV/u, it becomes important and leads to increase of 〈 q 〉 values by 3 – 5 times. Calculated average charges are in a good agreement with experimental data and semi-empirical estimates available at E = 132 keV/u and P = 0. 8 mbar. The 〈 q 〉 values are also compared with experimental data and other calculations for heavy and superheavy ions with atomic numbers Z = 38 – 114 as a function of the Bohr scaling parameter v Z 1 / 3 , where v is the ion velocity. • Calculations of atomic average charges need an account of the target-density effect. • Average charges of superheavy elements are well scaled with Bohr parameter v Z 1 / 3 . • The density effect shifts the equilibrium fractions towards higher ion charges. [ABSTRACT FROM AUTHOR]

The L-shell x-ray emissions of gold are investigated for the bombardment of high energy C6+ ions in the high energy region of 154.3–423.9 MeV/u. Due to the multiple ionization of outer-shell electrons at the movement of L x-ray emission, the blue shift of the experimental x-ray energy and an enhancement of the relative intensity ratios of Lι, Lβ–Lα x rays are observed. Using the improved thin target formula and considering the effect of multiple ionization on atomic parameters, the L-subshell x-ray production cross sections are extracted from the counts and compared with the theoretical estimations of BEA, PWBA and ECPSSR. It is found that the relative corrections of ECPSSR on PWBA can be ignored in the present experimental energy region. The calculations of PWBA and ECPSSR are almost identical and both are larger than the experimental results. The BEA is in better agreement with the experiment as a whole. [ABSTRACT FROM AUTHOR]

The cross-sections and Maxwellian rate coefficients of electron impact single ionization is theoretically investigated for tungsten ions (W64+ to W71+) for fine structure levels of configurations containing n = 2 orbitals. To check the accuracy of calculated cross-sections and rate-coefficients, detailed comparison between result from different approximations, binary encounter dipole (BED), distorted wave (DW) and coulomb born exchange (CBE) is presented. The calculations for electron impact ionization cross-sections of ground state are carried out for energy range 20 keV–1000 keV of final electron and Maxwellian rate coefficients for ground state are evaluated at the temperature range 20 keV–300 keV. We have also provided cross-sections at five different energies and rate-coefficients at five different temperatures. The present study of tungsten ions may be useful in fusion plasma modelling and in future comparison. • Electron impact ionization cross-section of tungsten ions are presented. • Maxwellian rate coefficients of tungsten ions are provided. • Electron impact ionization cross-sections are studied using BED, DW and CBE methods. • Maxwellian rate coefficients are studied using BED, DW and CBE methods. [ABSTRACT FROM AUTHOR]

Liquid crystal monomers (LCMs) are of emerging concern due to their ubiquitous presence in indoor and outdoor environments and their potential negative impacts on human health and ecosystems. Suspect screening approaches have been developed to monitor thousands of LCMs that could enter the environment, but an updated suspect list of LCMs is difficult to maintain given the rapid development of material innovations. To facilitate suspect screening for LCMs, in-silico mass fragmentation model and quantitative structure-activity relationship (QSPR) models were applied to predict electron ionization (EI) mass spectra of LCMs. The in-silico model showed limited predictive power for EI mass spectra, while the QSPR models trained with 437 published mass spectra of LCMs achieved an acceptable absolute error of 12 percentage points in predicting the relative intensity of the molecular ion, but failed to predict the mass-to-charge ratio of the base peak. A total of 41 characteristic structures were identified from an updated suspect list of 1606 LCMs. Multi-phenyl groups form the rigid cores of 85% of LCMs and produce 154 characteristic peaks in EI mass spectra. Monitoring the characteristic structures and fragments of LCMs may help identify new LCMs with the same rigid cores as those in the suspect list. [Display omitted] • A suspect list of 1606 LCMs is updated. • Multi-phenyl groups form the rigid cores of 85% of LCMs. • 41 characteristic structures representing rigid cores of LCMs were identified. • 154 characteristic ion peaks were identified in EI mass spectra of LCMs. [ABSTRACT FROM AUTHOR]

Calculations are performed for electron collision with the methylene molecular ion C H 2 + in its bent equilibrium geometry, with the goal of obtaining cross sections for electron impact excitation and dissociation. The polyatomic version of the UK molecular R -matrix codes was used to perform an initial configuration-interaction calculation on the doublet and quartet states of the C H 2 + ion. Subsequently, scattering calculations are performed to obtain electron impact electronic excitation and dissociation cross sections and, additionally, the bound states of the CH2 molecule and Feshbach resonances in the e - C H 2 + system. [ABSTRACT FROM AUTHOR]

The L-shell x-rays of Te have been measured for the impact of protons with energies from 100 to 300 keV, and He2+ ions in the energy range of 300–600 keV. The new experimental data of Te for individual L-subshell and total L x-ray production cross sections were extracted from the thick-target analysis of x-ray yields. This is significant for updating the existing database. The cross sections were also compared with theoretical calculations of BEA, PWBA, ECPSSR and ECUSAR along with various atomic parameter databases and including modification of multiple ionization. On the whole, The ECUSAR-MI predictions using Campbell's atomic parameters present a best agreement to the experimental data. [ABSTRACT FROM AUTHOR]

Rationale: Aminoindanes are one class of many new psychoactive substances that have emerged over the last decade. Analogues of 2-aminoindane (2-AI) are being encountered in crime laboratories and analytical data for most aminoindanes are limited. Interpretation and optimization of gas chromatography-mass spectrometry data will enhance reliability in characterizing aminoindanes. Methods: This study focuses on the electron ionization mass spectrometric fragmentation of eight aminoindane analogues and the gas chromatographic separation of these eight aminoindane analogues using four different column stationary phases, Rxi®-1Sil MS, Rxi®-5Sil MS, Rxi®-35Sil MS, and Rxi®-624Sil MS. Split injection (25:1) was utilized and each column had the same configuration (30 m x 25 mm x 0.25 µm), with the exception of the Rxi®-624Sil MS column (30 m x 25 mm x1.4 µm). Results: Mass spectra showed strong molecular ions for all aminoindanes, except for rasagiline that produced a uniquely abundant [M - 1] ion. Other characteristic fragmentation that was present for all the aminoindanes included indane and indene ions (m/z 115-117), the tropylium ion (m/z 91), and subsequent loss of diene to produce smaller ions that followed: phenyl (m/z 77), cyclopentadienyl (m/z 65), cyclobutadienyl (m/z 51), and cyclopropenyl (m/z 39). Conclusions: Separation of eight aminoindanes was optimized, and linear retention indices were determined for the compounds on four capillary columns. Based on the retention data, all eight aminoindanes were resolved on an Rxi®-624Sil MS column. Each aminoindane exhibited unique fragmentation ions in the mass spectra to distinguish between similar analogues. The results of this study will strengthen the analytical profiles of 2-AI and seven analogues, assisting forensic scientists in their analysis and identification of these substances. [ABSTRACT FROM AUTHOR]

Rationale: Systematic electron ionization fragmentation studies of steroids have been performed to elucidate and trace their characteristic fragmentation patterns. However, the electron ionization source setting at 70 eV electron energy is much higher than the ionization potential (7–15 eV) of most organic compounds, leading to extensive fragmentation. We present a multifactorial study on optimizing a low‐energy electron ionization source to maximize molecular ion formation while minimizing the extent of fragmentation to improve the analytical sensitivity of steroids, especially the more thermolabile ones, while preserving the information that can be extracted from the data. Methods: Twenty‐seven steroid reference materials, chosen to cover four main classes of urinary steroids, were considered; gas chromatography/quadrupole time‐of‐flight (GC/qTOF) analyses were carried out using an Agilent Technologies model 8890 gas chromatograph coupled to an Agilent Technologies model 7250 accurate‐mass quadrupole time‐of‐flight (GC/qTOF) instrument. The effects of electron energy, emission current, and source temperature, as well as their potential interactions on steroid fragmentation pathways, have been assessed in full factorial experimental designs. Results: Three parameters were specifically evaluated to improve the chromatographic/spectrometric response of the selected steroids: (i) degree of fragmentation; (ii) relative abundance of the molecular ion; and (iii) peak width. The first two were evaluated by screening designs that highlighted collision energy and source temperature as the most influential factors on the analytical responses of the considered steroids, while emission current always showed a non‐significant influence. Then, an optimization design was performed to select the final source setting by searching for the combination of factors that minimize peak tailing. Conclusions: The proposed analytical approach permits a faster selection of optimal experimental conditions for steroidomics analysis using low‐energy electron ionization and high‐resolution mass spectrometry. The development of these designs of experiments (DoE) in full factorial design (FFD) allowed multiple inputs to be monitored at the same time, highlighting the possible interactions and estimating the effects of a factor in the different levels of the other factors considered. [ABSTRACT FROM AUTHOR]

The article describes the results of a study of the effect of a supersonic gas jet on the formation and extraction of deuterium-substituted ions from a liquid supplied through a capillary into a radio-frequency quadrupole coupled to a time-of-flight mass spectrometer with orthogonal ion injection. The supersonic gas jet is formed inside a cylindrical channel and passes through an electron ionization ion source. With an increase in the flow rate of the a solution, there was no steady trend in the relative contributions of deuterated ions from the liquid phase. The results confirm the prospects of using a supersonic jet to create a high-performance source of deuterium-substituted ions from a liquid supplied into a vacuum region under residual pressure of 10–4 Torr without using strong electric fields. [ABSTRACT FROM AUTHOR]

The fragmentation of 5-[(cyanomethyl)sulfanyl]- and 5-[(1,3-dioxolan-2-ylmethyl)sulfanyl]-1H-pyrrol-2-amines under electron impact (70 eV) and chemical ionization with methane as reactant gas has been studied for the first time. Electron impact ionization of 5-[(cyanomethyl)sulfanyl]-substituted pyrroles generates low-stability molecular ions {M+·, Irel 4–22%; cf. Irel 16–69% for 5-[(1,3-dioxolan-2-ylmethyl)sulfanyl] analogs} whose primary fragmentation involves cleavage of the C–S bond with expulsion of NCCH2 radical. Other fragmentation pathways of the molecular ions include formation of [M – CHR4]+· ions (R4 = CN) and substituent decomposition products. The mass spectra of 5-[(1,3-dioxolan-2-ylmethyl)sulfanyl]pyrroles characteristically show [M – SCH2R4]+ ion peak. The most intense ion peaks in the chemical ionization mass spectra of 5-[(cyanomethyl)sulfanyl] derivatives are those of M+· (Irel 18–69%) and [M + H]+ (Irel 34–100%). Both 5-[(cyanomethyl)sulfanyl]- and 5-[(1,3-dioxolan-2-ylmethyl)sulfanyl]pyrroles decompose mainly through cleavage of the CH2–S and C5–S bonds with the formation of stable [M – CH2R4]+ (Irel 92–100%), [M + H – CH2R4]+· (Irel 22–75%), and [M + H – SCH2R4]+· ions (Irel 6–25%). [ABSTRACT FROM AUTHOR]

The one-step breakdown and derivatization of a panel of nine fentanyls to yield uniquely tagged products that can be detected by Electron Ionization Gas Chromatography-Mass Spectrometry (EI-GC-MS) is presented. The method involves the treatment of the synthetic opioids with 2,2,2-trichloroethoxycarbonyl chloride (TrocCl) at 60 °C for 3 h in dichloromethane and furnishes two products from one fentanyl molecule that can be used to retrospectively identify the original opioid. Parameters that were studied and fully optimized for the method included temperature, solvent, nature of scavenging base and reaction time. One of the two resulting products from the reaction bears the trichloroethoxycarbonyl (Troc) tag attached to the norfentanyl portion of the original opioid and greatly aids in the opioid detection and identification process. The methodology has been applied to the chemical modification of a panel of nine fentanyls and in all cases the molecular ion peak for the Troc-norfentanyl product bearing the distinctive trichloroethyl isotopic signature can be clearly observed. The method's LLOD was determined to be 10 ng/mL while its LLOQ was found to be 20 ng/mL. This methodology represents the first application of chloroformates in the chemical modification of this class of synthetic opioids that are notoriously inert to common derivatization strategies available for GC–MS analysis. [ABSTRACT FROM AUTHOR]

In this study, the gas-phase fragmentations of molecular ions of thioanisole derivatives were investigated using electron ionization mass spectrometry (EI-MS). In the EI-MS spectrum, a characteristic fragment ion [M − SH]+ was observed. The same result with the molecular ion of 3-aminothioanisole was enhanced, while the same phenomenon was not obvious in the EI-MS spectra of 2- or 4-aminothioanisole. To explain the fragmentation, we proposed a mechanism that involved the hydrogen transfer-induced S–C rearrangement with 3 pathways. Substituent effect results, deuterium-labelled experiments and density functional theory (DFT) calculations also confirmed the proposed mechanism. [ABSTRACT FROM AUTHOR]

A theoretical and computational study of photoionization of the one-electron molecular ion H 2 + initially in the 1 σ u state is performed. The laser pulse is linearly polarized with the carrier wavelength in the extreme ultraviolet and soft x-ray regions. The electron wave function is obtained by solving the time-dependent Schrödinger equation with the help of the generalized pseudospectral method. The dependence of the total ionization probability and photoelectron spectra on the orientation of the molecular axis is analyzed. Within the wavelength interval 6 to 23 nm, anomalous behavior of the ionization probability is found, where it increases with the angle between the polarization vector of the external field and the molecular axis and reaches a maximum at the perpendicular orientation of the molecule. The phenomenon is explained as resulting from the two-center interference in the wave function of the emitted electron. [ABSTRACT FROM AUTHOR]

We present relative cross section measurements of the inner-shell ionization of highly charged chromium ions by high-energy (7–30 keV) electrons. The measurements use a technique based on high-resolution X-ray spectroscopy, which correlates ionization events with Kα decay X-rays. Moreover, the measurements show that inner-shell ionization only affects the strength of the heliumlike 1s2s 3S1 → 1s2 1S0 forbidden line. The cross sections inferred for Li-like Cr21+ agree well with distorted wave calculations. [ABSTRACT FROM AUTHOR]

RATIONALE: Gas chromatography mass spectrometry (GC‐MS) with electron ionization (EI) is the most widely used analysis technique of gaseous samples, but it may be time‐consuming for online monitoring of mixtures whose concentrations relatively change rapidly. On the contrary, current ionization methods, such as chemical ionization (CI) and proton transfer reaction (PTR), also have some disadvantages such as selectivity. Therefore, appropriate soft ionization sources are searched for rapid online detection. METHODS: Hollow electrode capillary plasma ionization (HECPI) is based on single electrode plasma. A hollow capillary was placed as both the electrode and the inlet of the gaseous samples. The ionization source is coupled with a mass spectrometer for performance evaluation. RESULTS: Several typical compounds have been tested with HECPI‐mass spectrometer. In this process, the dominant ion peaks of all compounds can be indexed as molecular ion peaks, and the product ions of HECPI are less than that of dielectric barrier discharge ionization (DBDI). Three gaseous samples (linalool, triethylamine, and styrene) with various concentrations have been used to further confirm the performance of this source, and the detection limit of linalool is as low as 10 ppb. CONCLUSIONS: HECPI is simple in structure and shows good performance. The results also show that HECPI has the potential to be an effective tool for detecting online gaseous samples rapidly. [ABSTRACT FROM AUTHOR]

Rationale: 3‐Aroylbenzofurans and their 2‐nitrophenyl derivatives constitute fundamental intermediates for the synthesis of target compounds with pharmaceutical properties. However, their preparation via the Friedel–Crafts acylation of 2‐phenylbenzofurans, using Lewis acid as catalyst, often leads to mixtures of regioisomeric aroylbenzofurans that can be challenging to distinguish, thus preventing the reaction characterization. Method: We report a method for the unambiguous identification and differentiation of the desired 3‐benzoyl isomers from their 4‐ and 6‐regioisomers in a crude reaction mixture using gas chromatography coupled to multiple‐stage mass spectrometric (GC/MSn) analysis performed in collision‐induced dissociation (CID) mode. Results: Upon electron ionization, each set of isomers displayed nearly identical mass spectra. MSn revealed fragmentation patterns that varied in the location of the benzoyl group on the benzofuran scaffold: CID experiments performed on the molecular ion allowed the distinction of the 3‐acyl isomers from the 4‐ and 6‐regioisomers; CID experiments on the [M − Ar]+ ion allowed the distinction of the 4‐benzoyl from the 6‐benzoyl regioisomer, when the nitro group is located on the 2‐phenyl ring. Moreover, the unusual loss of OH• radical allowed ascertaining the position of the nitro group in 3‐acyl regioisomers bearing the NO2 group. The origin of the diagnostic OH• loss was investigated through MSn experiments using 18O‐labelled 3‐benzoyl derivatives. Conclusions: The method allows the rapid characterization of crude reaction mixtures of benzoylbenzofurans using solely GC/MSn analysis, simplifying the workflow of extensive isolation and purification for structure elucidation. [ABSTRACT FROM AUTHOR]

Equilibrium charge-state fractions F q and average charges 〈 q 〉 are calculated for low-charged Hf q + , W q + and Os q + ions with the charges q = 0–3 colliding with He atoms at energies E = 0.5–25 keV/u. F q and 〈 q 〉 values are obtained on the basis of electron-capture and electron-loss cross sections calculated by ARSENY and DEPOSIT codes briefly described in the paper. Calculated cross sections, F q and 〈 q 〉 values, calculated also for other low-energy ion–atom collisions, are compared with available experimental data. The present results may be of interest for specialists studying low-energy beams of rare isotopes of Hf, W and Os ions. [ABSTRACT FROM AUTHOR]

Electron-impact ionization cross sections are investigated for the ground levels of N 2 + and N 3 + ions. Additionally, the long-lived energy levels of the N 2 + 2 s 2 p 2 and N 3 + 2 s 2 p configurations are analyzed. Study includes both direct and indirect ionization processes. Contribution of the excitation–autoionization (EA) channels to the ionization cross sections is approximately 15% to 23% for both ions. Convergence of the EA cross sections is analyzed by considering excitations up to shells with the principal quantum numbers n ⩽ 20. The obtained results are compared to available experimental data for the N 2 + and N 3 + ions. • Indirect process contributes 15% - 23% for configurations of the N 2 + ion and long-lived levels of the N 3 + ion. • Excitations to shells with 11 ⩽ n ⩽ 20 produce up to ∼ 15% of the EA cross sections for the N 2 + ion. • Good agreement with measurements and the previous CADW and RMPS calculations is obtained for the N 3 + ion. [ABSTRACT FROM AUTHOR]

We study the single ionization of hydrogen and helium by the impact of a highly charged Coulomb projectile. To interpret the cross section we introduce a diagonal Padé approximant. We find that the use of a Padé [4, 4] describes the continuum distorted wave eikonal initial state theory within its range of validity very well. The nodes of the denominator of the Padé approximant give rise to four poles in the velocity complex plane: two in the upper plane and their conjugates in the lower plane. The dependence of these poles with the projectile charge can be reasonably fitted to give a closed form for the ionization cross section, resulting in a scaling very near to that of Janev and Presnyakov. The experiments available were described very well in its entire velocity range with the use of a Padé [8, 8], with four poles in the upper plane and their conjugates in the lower plane. We conclude that the poles of the Padé approximant seem to have all the information of the total ionization cross section. [ABSTRACT FROM AUTHOR]

Fragmentation of 1-alkyl(cycloalkyl, alkoxyalkyl)-5-[(alkyl, allyl, benzyl)sulfanyl]-1H-pyrrol-2-amines under electron impact (70 eV) and chemical ionization (with methane as reactant gas) has been studied for the first time. All the examined compounds under electron impact generated the molecular ion [M]+· (Irel 5–90%) whose primary fragmentation involved mainly cleavage of the C–S bond in the SR4 substituent with elimination of R4 radical (except for 1-isopropyl- and 1-cycloalkyl-1H-pyrrol-2-amines). The main pathway of the decomposition of 1-isopropyl(cycloalkyl)-N,N-dimethyl-5-[(methyl, allyl)sulfanyl]-1H-pyrrol-2-amines was cleavage of the C–N bond with both elimination of the R1 radical from the pyrrole nitrogen atom and fragmentation of the pyrrole ring through elimination of imine (or aziridine) molecule and formation of odd-electron [M – NR1]+· radical cation. Chemical ionization of the title compounds involved protonation, charge exchange, and electrophilic addition processes and elimination of Me (Et) and SMe (SEt) radicals from the [M + H]+ ions. [ABSTRACT FROM AUTHOR]