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Charge exchange has been recognized as a primary source of soft X-ray emission in many astrophysical outflow environments, including cometary and planetary exospheres impacted by the solar wind. Some models have been set up by using different data collections of charge-exchange cross-sections. However, multiple-electron transfer has not been included in these models. In this paper, we set up a charge-exchange model with the inclusion of double-electron capture (DEC), and make a detailed investigation of this process on X-ray emissions of highly charged carbon, nitrogen, oxygen, and neon ions by using available experimental cross-sections. We also study the effect of different n-selective cross-sections on soft X-ray emission by using available experimental n-distributions. This work reveals that DEC enhancement on line intensity is linearly proportional to the ratio of ion abundance in the solar wind. It is more obvious for soft X-rays from carbon ions (C4+) in collision with CO2, and the enhancement on line intensity can be up to 53 per cent with typical ion abundances [Advanced Composition Explorer (ACE)] in the solar wind. The synthetic spectra with parameters from the Ulysses mission for the solar wind reveal velocity dependence, target dependence, as well as the non-negligible contribution from the DEC.

The low-energy electron-scattering resonances of pyrene were characterized using experimental and computational methods. Experimentally, a two-dimensional photoelectron imaging of the pyrene anion was used to probe the dynamics of resonances over the first 4 eV of the continuum. Computationally, the energies and character of the anion states were determined using equation-of-motion coupled cluster calculations, while taking specific care to avoid the collapse onto discretized continuum levels, and an application of the pairing theorem. Our results are in good agreement with the predictions of electron-scattering calculations that include an offset and with the pyrene anion absorption spectrum in a glass matrix. Taken together, we offer an assignment of the first five electronic resonances of pyrene. Some of the population in the lowest-energy 2B1u resonance was observed to decay to the ground electronic state of the anion, while all other resonances decay by a direct autodetachment. The astronomical relevance of a ground-state electron capture proceeding via a low-energy resonance in pyrene is discussed.

Physical processes that result in the production of positive and negative ions are found to be interrelated. Evidence of this relationship is a correlation between the energies of molecule ionization and resonance production, found for a number of polycyclic aromatic hydrocarbons via the mass spectrometry of negative ions in resonance electron capture.

Resonant electron capture negative ion mass spectrometry (REC NI MS) is a highly informative method of investigation of low-energy electron-molecule reactions, thermochemistry, and kinetics of negative ion formation and decay. The review includes consideration of the physical principles and specific features of the method, a brief historical survey, terminological issues, and an outline of instrumentation. The potential of REC NI MS for solving structural and analytical problems is analyzed and the advantages of the method over classical positive ion MS are demonstrated. The results of analytical studies of organic and organoelement compounds using various types of mass spectrometers are reviewed. The reasons for low adoption of REC NI MS are analyzed and arguments are presented in favor of introducing the method into analytical practice as an additional tool implemented on the available instruments. Prospects for the development and improvement of REC NI MS for solving unconventional problems are discussed.

Up-conversion luminescence materials, such as NaYF4: Yb3+, Er3+ (Tm3+), have very promising application prospects in the biomedical field and have attracted continuous interest in recent years. However, their low up-conversion luminescence performance is still one of the key obstacles to their application. Herein, we have developed a simple and environment-friendly strategy to enhance the up-conversion luminescence of NaYF4: Yb3+, Er3+ (Tm3+) by combining carbon dots (CDs), which were obtained using a wheat straw as the starting material. This luminescence enhancement strategy was effective for different doping ions (NaYF4: Yb3+, Er3+ and NaYF4: Yb3+, Tm3+), different phase structures (cubic and hexagonal) and different morphologies (nanosphere, rod-like, and tube-like). The emission intensities at 539 nm increased around 322 times for tube-like CD@NaYF4: Yb3+, Er3+, 63 times for rod-like CD@NaYF4: Yb3+, Er3+, and 20 times for nanospherical CD@NaYF4: Yb3+, Er3+ compared with that of NaYF4: Yb3+, Er3+ without CDs. The mechanism of luminescence enhancement is probably due to the decrease in defects and the electron capture by CDs and transfer to the lower energy levels of Er3+ or Tm3+ ions.

In the present work, four, well-studied, model peptides (e.g., substance P, bradykinin, angiotensin I and AT-Hook 3) were used to correlate structural information provided by ion mobility and ECD/CID fragmentation in a TIMS-q-EMS-ToF MS/MS platform, incorporporating an electromagnetostatic cell (EMS). The structural heterogeneity of the model peptides was observed by i) multi-component ion mobility profiles (high ion mobility resolving power, R ~ 115–145), and ii) fast online characteristic ECD fragmentation patterns per ion mobility band (~ 0.2 min). Particularly, it was demonstrated that all investigated species were probably conformers, involving cis/trans-isomerizations at X-Pro peptide bond, following the same protonation schemes, in good agreement with previous ion mobility and single point mutation experiments. The comparison between ion mobility selected ECD spectra and traditional FT-ICR ECD MS/MS spectra showed comparable ECD fragmentation efficiencies but differences in the ratio of radical (•)/prime (ʹ) fragment species (H• transfer), which were associated with the differences in detection time after the electron capture event. The analysis of model peptides using online TIMS-q-EMS-ToF MS/MS provided complementary structural information on the intramolecular interactions that stabilize the different gas-phase conformations to those obtained by ion mobility or ECD alone.

We have studied ionization and electron capture cross sections for single-electron removal from biological molecules (adenine, cytosine, guanine, thymine, and uracil) by proton impact at energies ranging from 30 keV/amu to 10 MeV/amu. In this investigation, the three-body distorted wave method is used. The calculations are based on the independent electron model. For electron capture process, distortion in the final channel related to the Coulomb continuum states of the active electron and the projectile in the field of residual target ion is included. In case of ionization, we take all the pair-wise Coulomb interactions, which treat all interactions on equal footing in the final channel. Moreover, the asymptotic Coulomb logarithmic phase for the relative motion of two colliding nuclei is included in the initial channel. In both processes, the molecular character of the biological target is assumed to be a linear combination of their atomic orbitals (LCAO) and, for all cases, the different atomic orbitals are described with the Roothaan-Hartree-Fock (RHF) approximation. We have also calculated the total capture cross sections using simple Bragg’s additivity rule. For electron capture, the contributions to the TCS from the core orbitals of the molecule have also been explicitly analyzed. The double differential cross sections (DDCS) for electron emission as well as the total cross sections for single ionization of only uracil molecule with fast proton impact are also calculated. The results for capture and ionization cross sections are compared with other theoretical calculations and existing experimental data. We find that our calculated results are in quite better agreement with available experimental data than the other theoretical results.

Relative total ionization cross sections and fragment target ions have been measured for proton impact on CCl4 molecules for the first time, namely associated with the formation of CCl3+, CCl2+, CCl+, Cl2+, Cl+ and C+ ions. The experiment was conducted by crossing a proton beam of 2.5 to 10 keV with a CCl4 vapor target where the fragment ions were measured employing the time of flight technique. Relative fragment cross sections were added leading to the total relative cross section. All relative cross sections seem to be independent of the collisional energy. A qualitative comparison was conducted with previous measurements of electron impact experiments. Ratios of CCl3+/CCl2+, CCl3+/CCl+, CCl3+/C+ and CCl3+/Cl+ were compared to those obtained from electron impact experiments.

The generation of negative ions from SO2 in the gas phase was studied using the thermal surface ionization method. Six anion types were measured: O- , S- , SO- , and SO2- and anions with m/z=96 and m/z=128. The most abundant anion formed was S- and the formation routes are discussed for each of the six anions. O- , S- , and SO- are formed via dissociative electron attachment to the molecule, whereas the generation of SO2- and anions with m/z=96 and m/z=128 are probably associated with the formation of H2 SO4 in the gas inlet system and the ion source. Using statistical thermodynamics the dissociation temperatures of SO2 and SO in the gas phase are calculated and values of above 1800 °C are obtained for both molecules. We also estimated the optimal filament temperatures for the formation of all anions measured, indicating that for SO2 the optimal temperature is related to the electron affinity of the molecules: the optimal temperature increases with decreasing value of the electron affinity for the molecule corresponding to the respective anion.

Cross sections for target Ar K-shell ionization associated with single and double electron capture, as well as the same cross sections corresponding to projectile F K X-rays and the total cross sections for single and double capture, were determined for 1.8–2.2 MeV/u F 9 + , 8 + , 7 + projectiles. This work was performed at Western Michigan University using the tandem Van de Graaff accelerator. Coincidences between emitted X-rays and their corresponding charge-changed particles were detected. The Ar K X-ray coincidence cross section ratios for double to single capture are found to depend strongly on the incident charge state, with the ratios for F 9 + well exceeding unity. Possible explanations for this anomalous behavior are discussed but a conclusive explanation is not found. The results are compared to previous experiments using fully-stripped fluorine where coincidence techniques were not employed.

The number of priority and emerging contaminants nowadays exceeds several thousands. As a consequence, it is a daunting task to monitor thousands of compounds using classical gas chromatography–mass spectrometry (GC–MS). Preliminary non-targeted screening is thus usually performed to identify the most relevant contaminants. Here we analyzed complex environmental samples of snow, rain water and cloud water from the Arctic, France, Chile, and Russia by two-dimensional gas chromatography (GC × GC) with ionization methods including electron ionization (EI), positive chemical ionization (PCI), and electron capture negative ionization (ECNI) modes, combined with high-resolution mass spectrometry. This approach combines the separation capacity of GC × GC, detailed EI mass spectral libraries, the softness of PCI, and the selectivity of ECNI. Switching between ionization modes without any hardware change allowed to increase the information capacity and reliability of analysis. The structural elucidation becomes easier and more reliable due to the detection of molecular ions in PCI and ECNI modes with corresponding extensive fragmentation in EI, while the ECNI mode improves about 100 times the detection limits for environmentally relevant halogenated and nitro compounds. Overall, a notable enhancement of the analytical capabilities for both targeted and non-targeted purposes is achieved.

The method of collision spectroscopy, which is based on precision measurement of the kinetic energy of projectile ions after the electron capture process, is used to measure the partial cross sections of the formation of He+(n) ions in specific electronic states upon the capture of an electron by 3He2+ ions with energy E = 1.4–10 keV/a.m.u. from hydrogen atoms. A target of atomic hydrogen with a dissociation degree of 78% was created at the temperature of a tungsten dissociation cell of 2180 K.

An analysis is performed of the mass spectrum of resonance electron capture by tetracyanoquinodimethane molecules, in which long-lived negative molecular ions are detected. At 3.6 eV, the ions can be attributed to an electron-excited Feshbach resonance with an admixture of a long-lived ground state whose contribution to the superposition of two states yields a measurable ion lifetime in the microsecond range.

For a model series of nitro aromatic compounds comprising mono-, di- and trinitrotoluenes, and dinitrobenzene, using the same commercial experimental set up consisting of gas chromato-graphy/mass spectrometry (GC/MS) instrument equipped with a quadrupole analyzer, the two types of mass spectra were recorded, of positive ions (in the conventional, standard mode of electron ionization at 70 eV) and of negative ions (NI, generated at low, pre-ionization electron energies by resonant electron capture, REC). The comparative analysis of characteristic fragmentation processes was carried out for molecular ions of both signs. The sensitivity of REC NI MS method was established to enhance upon increasing the number of electron-withdrawing nitro groups, reaching or even outperforming that of the classical method of electron ionization (EI). Thus, the detection limit for trinitrotoluene in a solution was estimated as 5 ppm, which is by an order of magnitude lower as compared to the conventional EI mode of analysis. Comparison of the ion composition of NI mass spectra and of the relative intensities of ion peaks with the corresponding data obtained previously for the studied group of compounds by means of different types of mass spectrometers, has revealed a satisfactory inter-instrumental reproducibility of the NI mass spectra. The results reported herein indicate that the NI generation/registration mode, which can technically be readily available even without modifications of design of commercial GC/MS instrument in their basic configuration, is suitable to be introduced in laboratory practice as the additional tool for increasing the selectivity and reliability in detection/identification of trace amounts of compounds possessing a high electron af nity and for solving extraordinary structural and analytical problems.

he decomposition paths of tetraalkyl pyrophosphates under conditions of electron ionization in the mode of registration of positive ions correspond to the general pattern of fragmentation of phosphoric acids esters elucidated earlier by the authors. Electron ionization mass spectra in the mode of registration of negative ions by resonant electron capture are an effective means for extracting information on the number of carbon atoms in the alkyl radicals of tetraalkyl pyrophosphates and full esters of other phosphoric acids

Resonant mechanisms of electron–ion recombination accompanied by the formation of Rydberg atoms in a plasma containing atomic and molecular ions are investigated. An analytical approach is developed for the description of three-particle electron capture into a Rydberg state as a result of resonant energy transfer from a free electron to the electronic shell of a quasimolecular ion formed during the collision of an atomic ion with a buffer gas atom. An efficient method is proposed to calculate dissociative recombination rates under thermal excitation of all rotational–vibrational (rovibrational) levels of the molecular ion. The dependence of the cross sections and the rate constants of the processes on the principal quantum number is established, and the relative role of these processes is determined in a wide range of temperatures of the electron, Te, and gas, T, components of the plasma. Conditions are found under which integral contributions of the continuous spectrum of the molecule and of the whole rovibrational quasicontinuum to the total rate of resonant electron capture are dominant. A specific analysis is carried out by an example of Ne + Xe+ + e and Ar + Xe+ + e heteronuclear systems with significantly different dissociation energies (D0 = 33 and 171 meV) of the ground electronic term of the RgXe+ (Rg = Ne and Ar) ion. It is shown that the capture rate constants essentially depend on the binding energy |en| of the resulting Xe(n) atom, the temperatures T and Te, and the relationship between D0 and the thermal energy kBT.

The decay paths of negative molecular ions of phosphate esters, formed under the conditions of resonance electron capture, are of the same type and, therefore, predictable. A combination of mass spectra of the studied substances obtained by this method with the mass spectra of positive ions recorded in the convential electron ionization mode significantly expands the possibilities of their identification and determination of the characteristics of their molecular structures. In this case, only one mass spectrometer can be used, quickly switched from one mode to another.

Processes of the formation of negative ions during the resonance electron capture by molecules of cysteine and its N-substituted derivative are studied. The ion structures in the energy region

We report a new doorway mechanism for the dissociative electron attachment to genetic materials. The dipole-bound state of the nucleotide anion acts as the doorway for electron capture in the genetic material. The electron gets subsequently transferred to a dissociative σ*-type anionic state localized on a sugar-phosphate or a sugar-nucleobase bond, leading to their cleavage. The electron transfer is mediated by the mixing of electronic and nuclear degrees of freedom. The cleavage rate of the sugar-phosphate bond predicted by this new mechanism is higher than that of the sugar-nucleobase bond breaking, and both processes are considerably slower than the formation of a stable valence-bound anion. The new mechanism can explain the relative rates of electron attachment induced bond cleavages in genetic materials.

Lyman transitions of ${\mathrm{Xe}}^{53+*}$ produced by nonradiative electron capture in collisions of 95, 146, and 197 ${\mathrm{MeV/u}\phantom{\rule{4pt}{0ex}}\mathrm{Xe}}^{54+}$ ions with Kr and Xe atoms have been studied experimentally. It shows that the captured electrons preferentially populate lower states. The intensity ratios $I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\beta})/I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\alpha})$ and $I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\gamma})/I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\alpha})$ are found to decrease with increasing projectile velocity, and the ratios for Xe decrease faster than those of Kr. The obtained results are compared with the relative cross sections calculated with the relativistic eikonal approximation. For both targets, the theoretical results overestimate the experimental ratio $I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\beta})/I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\alpha})$ but underestimate $I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\gamma})/I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\alpha}).$ Moreover, the theory gives parallel decreasing curves for the two targets, which does not agree with the present experiment. In order to well understand the experimental findings, a more sophisticated theoretical approach is urgently required.

Radiative double-electron capture (RDEC), in which two-electron capture is accompanied by simultaneous emission of a single photon, was investigated for fully stripped and one-electron projectiles colliding with gaseous and thin-foil targets. RDEC can be considered the inverse of double photoionization by a single photon. For the gaseous targets, measurements were done for 2.11 MeV/u ${\mathrm{F}}^{9+}$ and ${\mathrm{F}}^{8+}$ ions interacting with ${\mathrm{N}}_{2}$ and Ne, while for the thin-foil target the measurements were done for 2.11 MeV/u ${\mathrm{F}}^{9+}$ and ${\mathrm{F}}^{8+}$ and 2.19 MeV/u ${\mathrm{O}}^{8+}$ and ${\mathrm{O}}^{7+}$ ions striking thin C targets. Reports on this work were already published separately in shorter accounts by La Mantia et al. [Phys. Rev. Lett. 124, 133401 (2020) for the gas targets and Phys. Rev. A 102, 060801(R) (2020) for the thin-foil targets]. The gas targets were studied under single-collision conditions, while the foil targets suffered unavoidable multiple collisions. The measurements were carried out by detecting x-ray emission from the target at ${90}^{\ensuremath{\circ}}$ to the beam direction in coincidence with outgoing ions undergoing double, single, and, in the case of the foil targets, no charge change inside the target. Striking differences between the gaseous and foil targets were found from these measurements, with RDEC for the gaseous targets occurring only in coincidence with q-2 outgoing projectiles as expected, while RDEC for the foil targets was seen in each of the outgoing q-2, q-1, and no charge-change states. The no charge-change result was totally unexpected. The cross sections for RDEC for the fully stripped ions on gas targets were found to be about six times larger than those for the one-electron projectiles. For the foil targets, the RDEC cross sections for the fully stripped and one-electron projectiles differ somewhat from one another but not to the the extent they did for the gas targets. In this work the cross sections for all of the projectiles for the foil targets were adjusted due to the target contaminant background from potassium and calcium atoms that existed in the spectra. Also, the cross sections for the incident one-electron projectiles were modified due to a correction for the fraction of these ions that becomes fully stripped in passage through the foil. These differences are attributed to the effects of the multiple collisions that occur for the foil targets. The differential cross sections at ${90}^{\ensuremath{\circ}}$ determined for each of the projectiles interacting with each of the targets are compared with each other and with the previous measurements. To the extent that the cross sections follow a ${sin}^{2}\ensuremath{\theta}$ dependence, the total cross sections are compared with theoretical calculations [E. A. Mistonova and O. Yu. Andreev, Phys. Rev. A 87, 034702 (2013)], for which the agreement is poor, with the measured cross section exceeding the predicted ones by about an order of magnitude. Possible reasons for this discrepancy will be discussed.

The K x-ray spectra of different targets (Cu, Zn, and Ge) induced by 3 to 5 MeV/u Si projectile ions have been measured to determine the K-shell ionization cross-section. A significant difference is observed between the measurements and theoretical estimates, with the latter being about 50% below the experimental results. This underestimation} is attributed to the charge-exchange from target K-shell to projectile K- and L-shells. Such observation can only be possible if the projectile ions attain up to H- and He-like charge states. Corresponding projectile charge state fractions have been evaluated from the Lorentzian charge state distribution, where mean charge state is taken from the Fermi gas model [Phys. Rev. Lett. 30, 358 (1973)] and width from the Novikov and Teplova approach [Phys. Lett. A378, 1286-1289 (2014)]. The sum of the direct ionization cross-section and K-K + K-L capture cross-sections gives a good agreement with the measured cross-sections. Furthermore, we have validated this methodology with available data for Si-ion on Ti target. Such results may be useful in many solid target based applications., Comment: 13 pages, 12 figures

Highly ionized heavy evaporation residues (ERs) resulting from heavy-ion (HI) fusion–evaporation reactions are knocked out from solid targets to rarefied gas of gas-filled recoil separators. In gas, these ERs undergo charge-changing collisions on their way to a detection system. An equilibrium between the loss of charge (electron capture) and the gain of charge (electron loss) for ionized ERs allows one to use equilibrated charge-state distributions in trajectory calculations for ERs moving through a magnetic field. The distance from a target to the point where the ER charge-state distributions become to be the equilibrated one is essential for such calculations. This distance can be estimated in simulations based on electron capture and loss cross sections for energetic HIs. Reasonable approximations of available experimental data have provided these cross sections, which were applied to the Monte Carlo simulations of the ionic charge evolution for highly ionized heavy ERs. The results of these simulations demonstrate the setting of charge equilibration close to the target.

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

Highly energetic ions traversing a two-dimensional material such as graphene produce strong electronic excitations. Electrons excited to energy states above the work function can give rise to secondary electron emission, reducing the amount of energy that remains the graphene after the ion impact. Electrons can either be emitted (kinetic energy transfer) or captured by the passing ion (potential energy transfer). To elucidate this behavior that is absent in three-dimensional materials, we simulate the electron dynamics in graphene during the first femtoseconds after ion impact. We employ two conceptually different computational methods: a Monte Carlo (MC) based one, where electrons are treated as classical particles, and time-dependent density functional theory (TDDFT), where electrons are described quantum-mechanically. We observe that the linear dependence of electron emission on deposited energy, emerging from MC simulations, becomes sublinear and closer to the TDDFT values when the electrostatic interactions of emitted electrons with graphene are taken into account via complementary particle-in-cell simulations. Our TDDFT simulations show that the probability for electron capture decreases rapidly with increasing ion velocity, whereas secondary electron emission dominates in the high velocity regime. We estimate that these processes reduce the amount of energy deposited in the graphene layer by 15\,\% to 65\,\%, depending on the ion and its velocity. This finding clearly shows that electron emission must be taken into consideration when modelling damage production in two-dimensional materials under ion irradiation., 14 pages, 8 figures

We report measurements of electron-impact excitation cross sections for the strong K-shell n=2-1 transitions in S XV using the LLNL EBIT-I electron beam ion trap, two crystal spectrometers, and the EBIT Calorimeter Spectrometer. The cross sections are determined by direct normalization to the well known cross sections of radiative electron capture, measured simultaneously. Using contemporaneous polarization measurements with the two crystal spectrometers, whose dispersion planes are oriented parallel and perpendicular to the electron beam direction, the polarization of the direct excitation line emission is determined, and in turn the isotropic total cross sections are extracted. We further experimentally investigate various line-formation mechanisms, finding that radiative cascades and collisional inner-shell ionization dominate the degree of linear polarization and total line-emission cross sections of the forbidden line $z$., 16 Pages, 9 Figures, published in ApJ

Final projectile charge states are experimentally and theoretically analyzed after ${\mathrm{H}}^{+}$ ions collide with a ${\mathrm{C}}_{60}$ monolayer deposited on Cu(111) with an ample range of incoming energies (2--8 keV) in the low-energy regime. The three possible charge states (negative, positive, and neutral) are experimentally measured by using the low-energy ion scattering technique for two different collisional setups: 45\ifmmode^\circ\else\textdegree\fi{} (90\ifmmode^\circ\else\textdegree\fi{}) and 67.5\ifmmode^\circ\else\textdegree\fi{} (67.5\ifmmode^\circ\else\textdegree\fi{}) incoming (exit) angles, relative to the target surface plane, with a fixed backscattering angle of 135\ifmmode^\circ\else\textdegree\fi{}. Experimental ion fraction magnitudes and energy dependence are practically intermediate between that found in pristine Cu(111) and a thick ${\mathrm{C}}_{60}$ film, revealing the influence of the substrate on the final charge state of the projectile. Unlike these previous systems, the positive and negative ions contribute nearly evenly to the total scattered charged particles. On the theoretical side, we applied a first-principles based model that considers the fine details of the surface under analysis and assumes a projectile trajectory corresponding to a single binary collision with the more exposed carbon atoms of the ${\mathrm{C}}_{60}$ molecule. The theoretical and experimental results are independently compared with the already reported cases: ${\mathrm{H}}^{+}$ on a thick ${\mathrm{C}}_{60}$ film, ${\mathrm{H}}^{+}$ on Cu(111), and ${\mathrm{H}}^{+}$ on graphite. A detailed analysis of the electronic surface band structure allows us to draw a conclusion about the relevance of the substrate in the present system and about the aspects to be improved in our theoretical description. The contrast between experimental and theoretical results allows us to infer that trajectories involving ion penetration and multiple scattering events are particularly relevant for the projectile-target charge exchange process studied.

The modified dipeptide, Captopril, was studied to determine the effect of lateral functional groups on the decay of biomolecules in resonant reactions of electrons with molecules. The main channels of fragmentation of negative molecular ions were determined, and the characteristic fragment ions were identified. The SH fragment of the lateral substituent of cysteine plays an important role similarly as does the carboxyl fragment of aspartic acid in oligopeptides.

At the Future Circular Collider (FCC-hh) at CERN in addition to proton-proton collisions it is planned to study interactions of 208Pb nuclei with the collision energy $$\sqrt {{{s}_{{NN}}}} = 39.4$$ TeV, which is 7–8 times higher than that achieved at the LHC. The electromagnetic dissociation (EMD) of $$^{{208}}$$ Pb nuclei, along with the electron capture resulting from the multiple production of e $$^{ + }$$ e $$^{ - }$$ pairs in ultraperipheral collisions at the LHC, lead to a significant luminosity decay, and secondary ions impose a well localized thermal load on superconducting magnets. As expected, such effects are reduced in collisions of light and medium nuclei. In the present work the EMD cross sections for collisions of $$^{{40}}$$ Ar, $$^{{40}}$$ Ca, $$^{{63}}$$ Cu, $$^{{78}}$$ Kr, $$^{{84}}$$ Kr, $$^{{115}}$$ In, $$^{{129}}$$ Xe, $$^{{208}}$$ Pb and $$^{{238}}$$ U at the LHC and the planned FCC-hh were calculated in order to assess the operation conditions of the colliders. The results were compared with results of the RELDIS model, and the uncertainties of calculations of the EMD cross sections associated with using of various approximations of the total nuclear photoabsorption cross sections were estimated.

A table-top electrostatic ion storage ring was constructed, and an argon ion ( Ar n + , n = 1, 2) beam was successfully stored. As an application of the storage ring, the electron capture cross section for a neutral Ar target was measured.

The absolute cross sections of single-electron capture and single-electron capture with dissociation in the interaction between incident He2+, C2+, N2+, and O2+ ions with energies from 6.4 to 36.4 keV and СО molecules were measured. It is demonstrated that the cross section of dissociative capture is much larger than the cross section of single-electron capture for O2+ projectile ions. A qualitative explanation for this effect is provided.

In this work, we report theoretical electron capture cross sections for single-electron removal from molecules of biological interest and noble gases by bare ion (H+ and He2+) impact at energies ranging from 25 to 10,000 keV/amu. We use a distorted wave (DW) method where the intermediate continuum state of the active electron with the target ion has been taken into account. This method is developed within the framework of the independent electron model taking particular care of the representation of the bound continuum target states. Two different approximations have been considered for molecular targets: molecular representation of the bound-state target wavefunction and Bragg’s additivity rule. The molecular orbital for targets are described within the framework of the complete neglect of differential overlap (CNDO) method based on the linear combination of atomic orbital (LCAO) approximation. Using the DW method, we have also calculated the K-, L- and M- shell electron capture in collisions of bare ions with three noble gases He, Ne, and Ar respectively. Contributions from different molecular orbitals and different shells to the total cross sections (TCS) are studied. The preference of electron capture occurs in accordance as the binding energy of the active electron in molecular orbital and atomic shell. The maximum contributions to TCS for SC comes from the less bound electrons in repetitive orbitals, whereas the tightly bound electrons dominate the TCS at higher projectile energy regime. Variation of TCS with impact energy are compared with the available experimental observation and other theoretical findings. We find that the present theoretical method is satisfactory in both intermediate and high-energy region for molecules as well as noble gas targets to give reliable outcomes compared to other theoretical methods.

The possibility of analytically calculating ion energy losses in the velocity interval of 1–10 au, where energy losses reach their maximum value, is considered. In this interval, the charge-exchange processes (electron capture and loss by an ion) lead to the fact that the average effective charge differs from the nuclear charge. The use of expressions for the average charge of ions passing through a carbon target in the Bethe—Bloch formula makes it possible to determine the ion velocities at which the energy losses reach their maximum and also the maximum ion energy losses. The performed calculations of the energy losses of ions with nuclear charges of Z = 4–10 agree quantitatively with the semiempirical (SRIM) and theoretical (PASS) results.

We have measured the absolute values of total cross sections of capture of one and two electrons by He2+ ions from argon atoms. The differential scattering cross sections have been determined for fast atoms and singly charged helium ions formed in each of these processes (without and with additional ionization of the formed slow argon ion). Measurements have been taken for He2+ ions with kinetic energy of 6 keV in scattering angle range 0–2.5°. Based on the measured differential cross sections using different model atomic particle interaction potentials, we have calculated the cross sections of these processes as functions of the impact parameter. The probabilities of realization of these processes with electron density distribution in different shells in the target atom have been compared. The applicability of the expressions for the screened Coulomb interaction potentials in the description of scattering of particles that have captured electrons has been demonstrated.

RATIONALE Charge transfer via DNA plays an important role in physical and chemical processes in biological systems, and is used in biomolecular electronics. The present study considers the resonant interaction of free electrons with nucleosides, which is important for an understanding of the processes of electron transport in DNA. METHODS Resonant electron capture negative ion mass spectrometry was used to study the processes of low-energy electron attachment to two uracil nucleosides, uridine and deoxyuridine, while density functional theory (DFT) calculations were used to analyze the energy aspects of ion formation and decay. RESULTS Short-lived molecular ions, formed via mechanisms of π* shape resonances, were found in the energy region below 5 eV. The fragmentation channels of these resonances and the structures of the charged and neutral products formed were determined. CONCLUSIONS These results suggest that the formation of some fragment negative ions occurs through intramolecular charge transfer.

Successful co-implementation of different heavy ion beam nuclear analytical techniques such as heavy ion PIXE, ERDA, MeV SIMS and RBS hinges on the availability of accurate databases of fundamental ion beam-matter interaction parameters. We report on measurements carried out to determine L-shell X-ray production cross sections in 101Ru and 181Ta due to 12C, 16O and 28Si projectile ions in the 0.2 MeV/u–1.0 MeV/u energy range. Experimental data is compared to calculations by one of the most widely implemented X-ray ionisation theories in PIXE analyses – the ECPSSR theory in its modified United Atom (UA) version. Results show fairly good agreement between experiment and theory for the 181Ta target atoms, with the level of agreement improving as the Zion/Ztarget ratio decreases and as beam energy increases. For 101Ru target atoms theoretical predictions tend to underestimate experimental data and the discrepancies increase with projectile mass and decreasing energy. The contribution of projectile electron capture (EC) to the measured X-ray production cross sections is also considered in the data analysis and discussion.

The mass spectrum of negative ions due to resonance electron capture by molecules of tetracyanoquinodimethane (TCNQ), a well-known electron acceptor, has been recorded in order to identify the dissociation processes of TCNQ molecular negative ions on the surface of an ionization chamber at thermal energies of electrons to be attached to the molecules. It has been found that the TCNQ molecular negative ions, preliminarily generated in the gas phase at several resonance maxima, reach the ionization chamber walls owing to a long extra-electron autodetachment lifetime ranging from 25 s in the first resonance at zero electron energy to 0.2 s in the resonance at 3.3 eV and dissociate at the walls as a result of the influence of the surface on the energy balance of the dissociation process. It has been taken into account that without the surface effect on the energy balance, this dissociation would be impossible because of an insufficient energy of the electron captured by the molecule. By B3LYP/6-311G calculations, the most probable dissociation pathways have been determined for negative fragment ions with various empirical formulas. The data obtained can be used to solve problems related to the properties of the TCNQ molecule in interaction with the conductive surface of a metal substrate in electronic devices.

The persistence of molecules to destruction under the action of low-energy (0–15 eV) electrons is investigated for a representative series of aromatic compounds of interest to organic electronics and photonics. The energy regions of the most effective interaction of free electrons with isolated molecules, which leads to the dissociative decay of molecules due to the formation of short-lived negative molecular ions unstable to fragmentation, are determined using resonance electron capture negative ion mass spectrometry. The characteristic fragmentation channels for molecular ions are revealed for some groups of compounds, and the threshold energies of the most significant fragmentation processes are estimated. Polycyclic aromatic hydrocarbons and oligophenyls are stable to the action of electrons in the electron energy range ~0–3 eV, above which these compounds are decomposed into the single channel of hydrogen atom detachment. For compounds with heterocycles (oxadiazole and maleimide derivatives) in their structure, the stability range narrows down to ~0–1 eV. Electrons with energies exceeding this range initiate the decay of molecules (anions) via various channels among which the detachment of a cyanate anion from a heterocyclic nucleus is the most intense and destructive process.

A model for the evaluation of charge-state distributions of fast heavy ions in solid targets is being developed since late eighties in terms of ETACHA code. Time to time it is being updated to deal with more number of electrons and non-perturbative processes. The calculation approach of the recent one, which is formulated for handling the non-perturbative processes better, is different from the earlier ones. However, the experimental results for the projectiles up to 28 electrons can be compared with the predictions from any versions of ETACHA code. Though earlier versions are not meant for the non-perturbative cases, but the detail comparison suggests that predictions from an earlier version is somewhat superior to that of the recent version. However, certain difference up to 4 units of charge found between the earlier version and experimental results on the mean charge states and charge state distributions is attributed to nonradiative electron capture taking place at the exit surface in the influence of wake and dynamic screening effects. This can be a possible mechanism of multiply charge formation in the electrospray ionization of big molecules., 22 pages, 10 figures

The charge state distributions of ions passing through gases or foils have a significant influence on the performance of AMS facilities. Most important is the stripping process in the terminal of the accelerator. Published data on charge state distributions have been collected as well as associated charge-changing cross sections for various projectiles and targets relevant to AMS. Based on these data, the stripping yields as function of the stripper thickness and ion energy are calculated. This allows to evaluate the stripping thickness required for reaching charge state equilibrium, as well as mass fractionation effects depending on energy and stripper thickness. The significantly different behavior of helium compared to other gases leads to very high stripping yields for specific charge states at low energies. The cross sections for electron detachment of negative ions give a tool for estimating beam losses in the low energy acceleration tube. Further, electron capture and loss cross sections allow the estimation of backgrounds caused by charge exchange processes in the acceleration tubes. The effects discussed here are illustrated with calculations and simulations for Carbon beams. The data are useful for the design of new AMS facilities or improving existing ones.

The effect of free–bound and bound–bound resonance nonadiabatic transitions of an electron on electron–ion recombination rates in the plasma of a Ne/Xe and Ar/Xe inert gas mixture has been studied. A kinetic model of recombination has been proposed including energy relaxation in collisions with electrons, resonant electron capture to Rydberg states through three-body collisions of Xe+ ions with Ne or Ar atoms and dissociative recombination of NeXe+ or ArXe+ ions, and n → n' resonance transitions. It has been shown that effective resonance processes occurring in quasimolecular systems sharply increase both the recombination coefficient and the effect of collisions with neutral particles even at quite high degrees of ionization of the plasma.

Two mechanisms of formation of long-lived negative molecular ions in TCNQ at resonant electron capture were considered for the case of the nonzero captured electrons. The first mechanism concerned with the ions lying in energy lower than the first molecular triplet was related to inter-systems crossing process providing formation of the long-lived ions with quartet multiplicity. The second mechanism, which yields high lifetime of the ions lying above the first triplet, was determined as a mixing of ion electronic states with the ground state contribution. The results give more knowledge of the long-lived negative ions formation.

A general quantum-mechanical formalism is reviewed for double electron capture from heliumlike atomic systems by fast nuclei. The development is carried out with and without the distorted wave theory by fulfilling the correct boundary conditions. These refer to the required asymptotic behaviors of the total scattering wave functions and their appropriate connections to the perturbation interactions that produce the transitions from the initial to the final states of the system. In this general formulation any choice is allowed for the pairs of the distorting potentials and the related distorted wave functions as long as the correct boundary conditions are satisfied. This is the case with the four-body versions of several most frequently used methods (continuum distorted wave: CDW-4B, boundary-corrected continuum intermediate state: BCIS-4B, Born distorted wave: BDW-4B, continuum distorted wave initial/final state: CDW-EIS/EFS-4B, and the boundary-corrected first Born: CB1-4B). A comparative analysis of these methods makes in evidence both their similarities and differences. For example, the most illustrative is the juxtaposition of the post BDW-4B and CDW-EIS-4B methods. They share the same distorting potential in the exit channel. The only difference is in the coordinates from the Coulomb logarithmic phases in the initial distorted wave functions. This difference is completely negligible in the asymptotic scattering regions. Yet, for e.g. double electron capture from helium by alpha particles, the total cross sections from these two methods differ by 1–3 orders of magnitudes. The BDW-4B method is in agreement with experimental data at high impact energies. In sharp contrast, within its validity domain of impact energies, the CDW-EIS-4B method underestimates the measured data by orders of magnitude. This shows that what matters is not solely the correct asymptotes of distorted wave functions, but rather how they affect the contributions to the integrals over the entire regions in the T-matrix elements for total cross sections. Such insights help understand the assessment of the overall validity and relative performance of various methods, and can provide a versatile guidance for improving the existing approximations for double charge exchange in fast ion–atom collisions.

We report the results of an ab initio study of resonant vibrational excitation of molecular oxygen by electron impact at low energies where the lowest-lying ${}^{2}{\mathrm{\ensuremath{\Pi}}}_{g}$ resonant state of ${\mathrm{O}}_{2}^{\ensuremath{-}}$ dominantly contributes to the cross sections. The contribution of this resonance to the dissociative electron attachment cross section is also determined and the origin of its unusual oscillations is discussed. Calculations were performed within the nonlocal resonance model describing the nuclear dynamics of ${\mathrm{O}}_{2}^{\ensuremath{-}}$ after electron capture into the resonant state. The model was constructed using potential-energy curves obtained with standard quantum-chemical methods and eigenphase sums from the fixed-nuclei $R$-matrix calculations of electron scattering off ${\mathrm{O}}_{2}$. The effect of the spin-orbit interaction is taken into account when determining the potential-energy curves of the molecular negative ion. The vibrational excitation cross sections are compared with other available theoretical and experimental results.

We calculated the cross section of double electron-positron pair production with two-electron capture for the collisions of Pb+Pb ions and we did our calculations at LHC energies. We applied a similar methodology for the calculation of bound-free electron-positron pair production. We used perturbation theory and implemented Monte Carlo integration techniques to calculate the lowest order Feynman diagrams. We also compared our double electron-positron pair production with two-electron capture cross section results obtained in the literature. These calculations may help us to learn more about strong QED., 7 pages, 1 figure

Astrochemical modelling has proposed that 10% or more of interstellar carbon could be tied up as polycyclic aromatic hydrocarbon (PAH) molecules. Developing reliable models of the interstellar carbon lifecycle requires calibration data obtained through laboratory studies on relevant chemical and physical processes, including on the photo-induced and electron-induced dynamics of potential interstellar PAHs. Here, the excited state dynamics of the S 1(ππ*) state of 2-naphthoxide are investigated using frequency-, angle-, and time-resolved photoelectron imaging. Frequency-resolved photoelectron spectra taken over the S 1(ππ*) band reveal low electron kinetic energy structure consistent with an indirect, vibrational mode-specific electron detachment mechanism. Time-resolved photoelectron imaging using a pump photon energy tuned to the 0-0 transition of the S 1(ππ*) band (hν= 2.70 eV) and a non-resonant probe photon provides the excited state autodetachment lifetime atτ= 130 ± 10 fs. There is no evidence for internal conversion to the ground electronic state or a dipole-bound state. These results imply that 2-naphthoxide has no resilience to photodestruction through the absorption of visible radiation resonant with the S 1(ππ*) band, and that electron capture by the S 1(ππ*) state, which is formally a shape resonance, is not a doorway state to a stable interstellar anion.

An theory of charge transfer at intermediate collision velocities is elaborated. Within the framework of the two-wave-function model, we analyze the intermediate stages of the population of the Rydberg states $$\nu _A=(n_A=8,l_A=0-2,m_A=0)$$ of highly charged ions escaping the target ion after atomic collision. The specificity of this approach is reflected in the time-symmetric description of the electron capture process by using two functions. The focus of the work is on determining the transition probabilities and corresponding rates whose analysis can be used to estimate the dominant partial neutralization distances at fixed initial and final states of the ion-ion system under consideration.