Successive Ionization Research Articles

Multicomponent dynamics of coupled quantum subspaces and field-induced molecular ionizations

To describe successive ionization steps of a many-electron atom or molecule driven by an ultrashort, intense laser pulse, we introduce a hierarchy of successive two-subspace Feshbach partitions of the N-electron Hilbert space, and solve the partitioned time-dependent Schrödinger equation by a short-time unitary algorithm. The partitioning scheme allows one to use different level of theory to treat the many-electron dynamics in different subspaces. We illustrate the procedure on a simple two-active-electron model molecular system subjected to a few-cycle extreme Ultra-Violet (XUV) pulse to study channel-resolved photoelectron spectra as a function of the pulse's central frequency and duration. We observe how the momentum and kinetic-energy distributions of photoelectrons accompanying the formation of the molecular cation in a given electronic state (channel) change as the XUV few-cycle pulse's width is varied, from a form characteristic of an impulsive ionization regime, corresponding to the limit of a delta-function pulse, to a form characteristic of multiphoton above-threshold ionization, often associated with continuous-wave infinitely long pulse.

Solid-state UV–MALDI–MS assay of transition metal dithiocarbamate fungicides

The determination of transition metal containing dithiocarbamate fungicides represents a challenging aspect of analytical object. They have a low stability, low solubility and stabilize versatile coordination monomers, dimers, disulfides and/or S-oxidized derivatives. Their diverse biological activities and agricultural implementation encompass plant prevention and crop protection against a variety of plants containing fungi and diseases of 400 pathogens and 70 cultures. Nonetheless, those dithiocarbamates (DTCs) are banned for agricultural use in Europe or have expiration at years2016-2017 because of their highly toxic degradation products and/or metabolites, in particular ethylene thiourea; they found large-scale implementations in materials research and medicine. Despite the broad interdisciplinary of DTC application, due to the above reasons, they have received little attention in the rapidly growing field of analytical chemistry, and in particular, the analytical mass spectrometry. Therefore, the study reported on qualitative, quantitative and structural analysis of ten DTCs (1-10), using the matrix assisted laser desorption/ionization (UV-MALDI)-Orbitrap-mass spectrometry (MS) contributed considerably to the implementation of the method for environmental and foodstuffs monitoring. Its ultrahigh resolving power and capacity for direct solid-state analysis, at limited number of sample pretreatment steps, at concentration levels of analytes of up to femtogram per gram resulted to achievement of a highly precise analytical information for these non-trivial objects. The presented fully validated method and technique is based on the successful ionization of DTCs embedded in three novel organic salts (M1-M3). In this regard, the reported MS and the single-crystal X-ray diffraction data as well as the quantum chemical one are able to correlate the molecular structures in condense and in the gas phase. Despite the novelty of the fundamental methodological character of the research reported, the promising metrology contributed to the applied aspect of the UV-MALDI-MS as a robust analytical method for environmental and foodstuffs monitoring, which is tested on two commercially available crop protecting products such as Mancozeb® and Antracol®, respectively.

Generation of picoliter droplets of liquid for electrospray ionization with piezoelectric inkjet

We report the association of inkjet and electrospray ionization MS to detect picoliter droplet, where the liquid volume and its position onto the tip can be precisely controlled to form ultrafine droplets for successive ionization of the analyte. Single rectangle pulse was applied to piezoelectric device on inkjet microchip for the ejection of each picoliter droplet, and it was controlled by a computer. The voltage and width of driving pulse for the inkjet were optimized to make reproducible ejection of the solvent with low viscosity. The volume of each droplet was about 600 pl, and a trigger of 10 droplets was selected as the best inlet mode taking relative standard derivation of the droplets into consideration. The target substrate used with high voltage to form ionization was graphite, after several attempts with some materials. High-speed camera was used to capture the breaking-up process of a droplet. The distance between the inkjet nozzle and the tip was set at 2 cm to avoid short circuit. The influences on the mass intensity of the diameter of the tip, the volume and the concentration of the sample were examined. The tip with a small diameter performed greater intensity, and the limit of detection decreased, whereas the small volume of liquid played high ionization efficiency. Linear regression in the range between 1 and 200 ppm for caffeine was conducted, where internal standard theobromine was used. Some real samples were also detected with the instrument.

A novel UV-MALDI-MS analytical approach for determination of halogenated phenyl-containing pesticides

The paper highlighted the capability of the UV-MALDI mass spectrometry, employing the Orbitrap analyzer for solid-state assay of halogenated phenyl–pesticides in mixtures. It is successfully applied for the analysis of eighteen (1)–(18) molecular objects of Fenarimol (1) type and their condensation products (P5)–(P12). The full method and technique validation is performed using the dried droplet sample preparation technique on embedded analytes in novel organic matrix crystals of N-(1H-benzoimidazol-2-yl)-guanidine (M4) and (E)-phenyl-2-pyridyl ketone oxime (M5), resulting to successful ionization of the analytes. Since the sampling technique in the UV-MALDI method is a key step in the overall process impacting significantly the metrology through the reproducibility of the data, the crystallization of M4, M5 and matrix–analyte in situ morphology of the samples is controlled by single crystal X-ray diffraction. The achieved promising metrology of LODs, of 0.46ngkg−1 (1.53ngkg−1 LOQs), is several orders of magnitude lower than the reported ecotoxicological effect values of studied pesticides. It is confirmed by the partial validated protocol based on ESI-MS. Inasmuch that LC-MS/MS is a method of choice for foodstuffs monitoring of organic contaminations, due to its routine quantitative analytical procedures, it is often characterized with the difficulties of the chromatographic separation of the closely structured analytes at a large scale of experimental conditions, complex multi-step sampling pretreatments, which inevitably alert the variables through the systematic and random errors. In this respect, notwithstanding the complex quantitative UV-MALDI-Orbitrap-MS procedure, conceptually different from the LC-MS/MS one, its high resolving power, capability for achieving meaningful analytical qualitative, quantitative and structural information of low-molecular weight analytes, its instrumental and sampling operation flexibility, applicable for a large scale of foodstuff matrices, and operating at the analyte concentrations of up to fgg−1 make UV-MALDI-Orbitrap-MS a perspective method of choice for an extensive implementation in the foodstuffs monitoring practice for control of the most essential task related to the assessment of the human health risks from environmental and foodstuff contaminations.

First successful ionization of Lr (Z = 103) by a surface-ionization technique

We have developed a surface ionization ion-source as part of the JAEA-ISOL (Isotope Separator On-Line) setup, which is coupled to a He/CdI2 gas-jet transport system to determine the first ionization potential of the heaviest actinide lawrencium (Lr, Z = 103). The new ion-source is an improved version of the previous source that provided good ionization efficiencies for lanthanides. An additional filament was newly installed to give better control over its operation. We report, here, on the development of the new gas-jet coupled surface ion-source and on the first successful ionization and mass separation of 27-s (256)Lr produced in the (249)Cf + (11)B reaction.

Identification of first order and non-first order contributions in the (e,3–1e) and (e,3e) double ionization of molecular nitrogen

Double ionization of nitrogen molecules is investigated in coplanar asymmetric (e,3–1e) and (e,3e) experiments. The measurements are performed at intermediate incident energy (∼600 eV) with one fast scattered electron and two slower ejected electrons sharing equally the excess energy. The data are compared with the predictions of a simple kinematical model recently reported by Lahmam-Bennani et al (2010 J. Phys. B: At. Mol. Opt. Phys. 43 105201) which describes the ‘two-step 2’ (TS2) mechanism as two successive (e,2e) single ionization interactions. The model is extended to include binary as well as recoil scattering during the two successive single ionization events. It is shown to qualitatively predict the correct angular positions for most of the observed structures. Moreover, the (e,3e) data are compared with the predictions of a first Born model which fails to reproduce the experimental angular distributions. These results demonstrate that the molecular double ionization process is largely dominated by the TS2 mechanism, as was the case in our previous works on atomic targets.

Concerning electronegativity as a basic elemental property and why the periodic table is usually represented in its medium form

Electronegativity, described by Linus Pauling described as “The power of an atom in a molecule to attract electrons to itself” (Pauling in The nature of the chemical bond, 3rd edn, Cornell University Press, Ithaca, p 88, 1960), is used to predict bond polarity. There are dozens of methods for empirically quantifying electronegativity including: the original thermochemical technique (Pauling in J Am Chem Soc 54:3570–3582, 1932), numerical averaging of the ionisation potential and electron affinity (Mulliken in J Chem Phys 2:782–784, 1934), effective nuclear charge and covalent radius analysis (Sanderson in J Chem Phys 23:2467, 1955) and the averaged successive ionisation energies of an element’s valence electrons (Martynov and Batsanov in Zhurnal Neorganicheskoi Khimii 5:3171–3175, 1980), etc. Indeed, there are such strong correlations between numerous atomic parameters—physical and chemical—that the term “electronegativity” integrates them into a single dimensionless number between 0.78 and 4.00 that can be used to predict/describe/model much of an element’s physical character and chemical behaviour. The design of the common and popular medium form of the periodic table is in large part determined by four quantum numbers and four associated rules. However, adding electronegativity completes the construction so that it displays the multi-parameter periodic law operating in two dimensions, down the groups and across the periods, with minimal ambiguity.

Exploring Interatomic Coulombic Decay by Free Electron Lasers

To exploit the high intensity of laser radiation, we propose to select frequencies at which single-photon absorption is of too low energy and two or more photons are needed to produce states of an atom that can undergo interatomic Coulombic decay (ICD) with its neighbors. For Ne(2) it is explicitly demonstrated that the proposed multiphoton absorption scheme is much more efficient than schemes used until now, which rely on single-photon absorption. Extensive calculations on Ne(2) show how the low-energy ICD electrons and Ne(+) pairs are produced for different laser intensities and pulse durations. At higher intensities the production of Ne(+) pairs by successive ionization of the two atoms becomes competitive and the respective emitted electrons interfere with the ICD electrons. It is also shown that a measurement after a time delay can be used to determine the contribution of ICD even at high laser intensity.

Two-Step Matrix Application for the Enhancement and Imaging of Latent Fingermarks

Matrix deposition is a crucial aspect for successful matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) analysis. The search for more efficient protocols over the years has resulted in the devising of "dry matrix methods" in which the matrix is solely or preliminarily deposited as powder and acts in most cases as a seeding agent. Although not fully embraced by the MALDI MSI community, these methods have proven to be more efficient in terms of ion intensity, ion abundance, and ion images in the experimental circumstances they were employed. Here we report a novel two-step matrix application method, that we have named the "dry-wet" method, where the matrix is dusted onto the sample followed by solvent spray using a robotic device. The new method has been successfully applied to the detection and mapping of several analyte classes within latent fingermarks. Dusting the matrix generated the added advantage of enhancing the latent fingermarks which are invisible. This allows not only for an optical image to be taken of the fingermark in situ but also bridges the gap in the application of MALDI MSI technology in this field; with the use of the methodology reported, fingermark enhancement, recovery, and analysis from different surfaces is now compatible with subsequent MALDI MSI analysis thus allowing visual and chemical information to be obtained simultaneously.

Oxygen atoms and molecules atLa1−xSrxMnO3surfaces

A localized description, rather than energy bands, is appropriate for the manganite substrate. Empty substrate levels lower in energy than occupied oxygen levels indicate need for further terms beyond the local density approximation. So also does van der Waals interaction between the two. Methods to include both are suggested by related, exactly soluble, two-electron problems. The descriptions of the electronic structure of the molecule and a ${\text{La}}_{1\ensuremath{-}x}{\text{Sr}}_{x}{\text{MnO}}_{3}$ (LSM) substrate are greatly simplified to allow incorporation of these effects and to treat a range of problems involving the interactions between oxygen atoms, or oxygen molecules, and such a substrate. These include elastic impacts, impacts with electronic transitions, and impacts with phonon excitation. They provide for capture of the atoms or molecules by the surface, leaving the neutral molecule strongly bound over a ${\text{Mn}}^{4+}$ site. It is found that oxygen vacancies in LSM diffuse as a neutral species and can appear at the surface. Bound molecules tend to avoid sites next to vacancies but, if there, should drop one atom into the vacancy leaving the remaining triplet oxygen atom bound to the resulting ideal surface, with no need for spin flips nor successive ionization steps.

Injection and Trapping of Tunnel-Ionized Electrons into Laser-Produced Wakes

A method, which utilizes the large difference in ionization potentials between successive ionization states of trace atoms, for injecting electrons into a laser-driven wakefield is presented. Here a mixture of helium and trace amounts of nitrogen gas was used. Electrons from the K shell of nitrogen were tunnel ionized near the peak of the laser pulse and were injected into and trapped by the wake created by electrons from majority helium atoms and the L shell of nitrogen. The spectrum of the accelerated electrons, the threshold intensity at which trapping occurs, the forward transmitted laser spectrum, and the beam divergence are all consistent with this injection process. The experimental measurements are supported by theory and 3D OSIRIS simulations.

Ionization potentials and conditional amplitudes

A procedure for deriving ionization potentials is presented based upon the factorization of a wave function into the product of a conditional amplitude and a one-electron marginal amplitude. In the asymptotic limit as one electron is removed, the conditional amplitude becomes the wave function of the residual positive ion, so that successive ionization potentials can be generated in sequence by the same procedure.

Koopmans' approximation applied in atoms and diatomic molecules using the diffusion quantum Monte Carlo method

AbstractKoopmans' theorem was applied to generate trial wave functions for ions from neutral systems and further applied in the determination of vertical ionization energies using the diffusion quantum Monte Carlo (DQMC) method. The results for successive and conventional ionization energies for atoms and diatomic molecules using the Slater minimum basis set with polarization wave functions indicate that DQMC provides a significant quantity of relaxation and electronic correlation effects. The conventional ionizations for core electrons calculated with DQMC for atoms and diatomic molecules yielded an average deviation of around 2–3 eV from the experimental results, which is excellent when compared with a deviation of around 17 eV estimated from Koopmans' theorem. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Determination of electron temperature based on a semicoronal model in Hall accelerator plasma flows

We present the results of a spectroscopic study of a nonequilibrium plasma in a Hall accelerator, in particular for such an important parameter as the electron temperature. For the studied conditions, we used the semicoronal equilibrium model, which relates the intensity ratios for two successive ionization steps for the same element.

Analysis of amitrole by normal‐phase liquid chromatography and tandem mass spectrometry using a sheath liquid electrospray interface

The coupling of normal-phase liquid chromatography to tandem mass spectrometry, previously developed in our laboratory, has been applied to the analysis of amitrole. This coupling utilizes an electrospray interface modified to accommodate the introduction of a make-up solution at the tip of the electrospray probe. A methanolic solution containing 3 mM ammonium acetate delivered at a flow rate of 10 microL . min(-1) was found to be the optimal sheath liquid to promote successful ionization of the amitrole. Protonated molecules, arising from in-source dissociation of ammonium adducts, were subjected to tandem mass spectrometric experiments in a triple-quadrupole instrument. The main fragmentation reactions were characterized and selected to acquire chromatographic data in the multiple reaction monitoring mode. The limit of detection for amitrole was in the ppm range without any preconcentration step. Enhanced efficiency of ion transmission achievable nowadays in mass spectrometers (this analytical configuration was developed with a 15-year-old instrument) is reasonably expected to further improve this detection level.

Investigation of plasma-related matrix effects in inductively coupled plasma-atomic emission spectrometry caused by matrices with low second ionization potentials—identification of the secondary factor

Plasma-related matrix effects induced by a comprehensive list of matrix elements (a total of fifty-one matrices) in inductively coupled plasma-atomic emission spectrometry were investigated and used to confirm that matrix effects caused by elements with a low second ionization potential are more severe than those from matrix elements having a low first ionization potential. Although the matrix effect is correlated unambiguously with the second ionization potential of a matrix, the correlation is not monotonic, which suggests that at least one other factor is operative. Through study of a large pool of matrix elements, it becomes possible to identify another critical parameter that defines the magnitude of the matrix effect; namely the presence of low-lying energy levels in the doubly charged matrix ion. Penning ionization by Ar excited states is proposed as the dominant mechanism for both analyte ionization/excitation and matrix effects; matrices with a low second ionization potential can effectively quench the population of Ar excited states through successive Penning ionization followed by ion-electron recombination and lead to more severe matrix effects.

Core Relaxation in Atomic Ultrastrong Laser Field Ionization

We have investigated atomic ionization dynamics in Kr in the transition regime from nonrelativistic to relativistic laser intensities (10(16) to 10(18) W/cm2) by measuring yields of highly charged ions stemming from an inner shell. Interpretation of the data is focused on the applicability of the single active electron description, which requires fully relaxed core states between successive ionization steps. In particular, we are concerned with transient core polarization or alignment effects originating from the strong dependence of the ionization rates on the magnetic quantum number. We found that for intense laser pulses with 40 fs pulse width internal m-mixing processes appear to be sufficiently fast to erase any transient core polarization.

Thermal and non-thermal fragmentation of xenon cluster ions

The internal temperature and decay rate of free evaporating neutral and ionized xenon clusters have been calculated as a function of their size at the same moment. These functions are substantially different for the neutral and ionized clusters. In a wide range of the initial internal temperature, acquired by the neutrals in the process of the cluster formation, the results do not depend on this temperature. However, the temperature range and criterion were found, on which the results do depend. The time evolution of the decay of electron-impact ionized xenon clusters (up to 5000 atoms) has been experimentally studied in pulsed jets by the retarding potential method. Calculated properties of the evaporating fragmentation have permitted to show that non-thermal fragmentation of xenon cluster ions exists in parallel with the thermal one. With a decrease in the cluster size, the probability of the non-thermal fragmentation of xenon cluster ions increases as compared with the probability of the thermal evaporation, in agreement with the model proposed earlier. The threshold time of the non-thermal fragmentation of xenon cluster ions was found to be substantially larger as compared with that of argon cluster ions. The non-thermal fragmentation of xenon cluster ions is not due to the successive single ionization of two atoms. Ionization into the excited ion states stimulates fragmentation of the clusters.

Coulomb explosion of large polyatomic molecules assisted by nonadiabatic charge localization.

The electron-nuclear dynamics of the Coulomb explosion of a large polyatomic molecule, anthracene, is probed using kinetic energy distributions of produced H+ ions. The kinetic energy release of ejected protons exceeds 30 eV for anthracene exposed to 10(14) W cm(-2), 800 nm pulses of 60 fs duration. We propose a strong-field charge localization model, based on nonadiabatic dynamics of charge distribution in a (multiply) ionized molecule; the charge localization lasts many laser periods and is sustained through successive ionizations of the molecular ion. The model explains quantitatively the dependence of the H+ kinetic energy on the laser intensity. Dissociative ionization of a polyatomic molecule enabled by long-lived charge localization is a new type of electron-nuclear dynamics and is essential for understanding the pathways of molecular or ionic fragmentation in strong fields.

Weakest bound electron potential model theory

AbstractDiffering from the self‐consistent field (SCF) method, in which an N‐electron atom problem is treated as a one‐electron problem with the use of a basic assumption of average potential, we develop a unified weakest bound electron potential model (WBEPM) theory. The relativistic form of the theory is given for the first time and is combined with the nonrelativistic form introduced in previous work to arrive at the unified WBEPM theory. The theory has two main ideas. First, from consideration of viewpoints of the dynamic successive ionization and the choice of zero of energy in quantum mechanics, an N‐electron atom system can be subdivided into N subsystems only containing a weakest bound electron (WBE) in each of subsystems. For each subsystem by separation of WBE and non‐weakest bound electrons (NWBE), WBE is believed to move in an approximate potential field provided by a “core” consisting of NWBEs and the nucleus. Thus, a complicated N‐electron problem is reduced to a simple analytical one‐electron problem of WBE. Second, the properties of an atom, such as total wave function, total energy, atomic energy levels, and transition between energy levels, can be investigated through the behaviors of a WBE or several WBEs, or up to all WBEs. Several excellent illustrative results show that the theory is capable of attaining very good computational accuracy. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004