Doubly-charged Ions Research Articles

Surface-induced dissociation and reactions of cations and dications C 7H 8[rad]+/2+, C 7H 7+/[rad]2+ and C 7H 62+: Dependence of mass spectra of product ions on incident energy of the projectiles

Surface-induced dissociation and reactions of singly-charged ions C 7H n + ( n = 8, 7) and of doubly-charged ions C 7H n 2+ ( n = 8, 7, 6), produced by electron ionization of toluene, with hydrocarbon-covered stainless steel surface have been investigated in the incident energy range from 5 to 50 eV. The mass-selected beam of projectile ion was focused onto the surface under 45° and product ions reflected were monitored using a TOF mass spectrometer. The relative abundance of product ions was determined in dependence on incident projectile-ion energy (collision-energy resolved mass spectra, CERMS curves). An important process in surface collisions of the dications is single-electron exchange with the surface and formation of monocation intermediates. Comparison of the mass spectra of the incident cations and dications made it possible to elucidate major reaction pathways.

GaBi alloy liquid metal ion source for microelectronics research

A GaBi alloy liquid metal ion source has been studied. From an analysis of the source mass spectra as a function of emission current, a mechanism is suggested for the production of single- and double-charged ions. There is good agreement with the results of Swanson's investigations of a pure Bi source.

Observation of high-lying weak autoionizing resonances of Ne, Na, and Mg atoms by charge-separated photoion-yield method

Doubly-excited 2s−12p−13pnp autoionizing resonance series of Ne atom as well as autoionizing resonances in the 2s region of Na and Mg atoms have been studied with monochromatized synchrotron radiation. Use of charge-separated photoion-yield method allowed us to detect these weak resonances in a clarified way in the yield curves of doubly-charged ions. The observed resonance states have been interpreted with the help of MCDF calculations, and the decay processes of these resonance states are discussed briefly.

Modelling dications in the diurnal ionosphere of Venus

Context.Previous studies have shown that doubly-charged positive ions, including molecular ions, can have detectable densities in the ionospheres of Mars, Titan, and the Earth. Aims.In the present paper, we continue our approach by modelling the Venusian ionosphere. The neutral atmosphere of Venus has a similar composition to the ones encountered in the other terrestrial planets, with carbon dioxide (as on Mars), nitrogen (as on Earth and Titan), and atomic oxygen (as on Earth). Methods. We computed the doubly-charged positive ion production through photoionisation (primary production) and electron impact ionisation (secondary production). We computed the densities under the photochemical equilibrium assumption. Results. We predict a ${\rm CO_2}^$ layer centred around $140~{\rm km}$ altitude with a density reaching 30 dications per ${\rm cm}^{3}$ in active solar conditions and a ${\rm N_2}^$ layer centred around a $140{-}150~{\rm km}$ altitude with density reaching $0.3~{\rm cm}^$. We find good agreement between the modelled ${\rm O}^$ densities and Pioneer Venus Orbiter measurements. Finally, we investigate the problem of possible detection of these ions by the European spacecraft Venus Express. Conclusions. Although molecular doubly-charged positive ion densities are low, these ions cannot be considered as negligible compared to other minor ion species. Their detection should be possible in the future through remote sensing or in-situ methods including ion mass spectrometry and UV spectroscopy.

ヘリウムグロー放電イオン源における高効率イオン化に対する一考察

High-effective ionization during ferrous analyses using a He glow-discharge ion source was investigated. The respective relationships between the ionization potential (Ip) of each element and various ionic strengths were studied in detail for He glow discharge and Ar glow discharge. The energies of the helium metastable atom (Hem) is 1910 kJ/mol (19.80 eV) and 2022 kJ/mol (20.96 eV). It is presumed that Hem contributes to creation of doubly-charged and singly-charged ions. Results show that numerous doubly-charged ions are generated by He glow discharge. If this ratio is greater than that of an internal standard element Fe, the RSF-value becomes greater than 1 (the ionic strength ratio decreases). Furthermore, with elements having Ip2 of more than approximately 18 eV, e.g., Ni, As, P, and C, the relative ionic strength of doubly-charged ion with respect to the singly-charged ion is only several percent at the highest. Consequently, the RSF-values approach unity (1). High-effective ionization by glow discharge is dependent upon the type of discharge gas, the matrix (internal standard element) and analyzing element, the presence of spectral interference, RSF-value, and other factors.

High precision titanium isotope measurements on geological samples by high resolution MC-ICPMS

A method has been developed for the precise and reproducible measurement of Ti isotopes in natural materials using high resolution MC-ICPMS. Instrumental mass fractionation is internally corrected using 49Ti/ 47Ti. Replicate measurements of synthetic standard solutions, terrestrial rocks, and the carbonaceous chondrite Allende yield a long-term reproducibility (2 σ) of 0.28 ɛ, 0.34 ɛ, and 0.28 ɛ for 50Ti/ 47Ti, 48Ti/ 47Ti, and 46Ti/ 47Ti, respectively. Isobaric interferences from 46,48Ca +, 50V +, 50Cr +, and doubly charged Zr can be corrected for reliably in separated Ti solutions with Ca/Ti < 5, V/Ti < 0.3, Cr/Ti < 0.2, and Zr/Ti < 1, respectively. Such elemental ratios are achieved easily in most samples using the anion-exchange procedure presented. Single and double charged polyatomic ions can either be resolved, e.g., 14N 36Ar +, or do not compromise the measurements. The method has been successfully applied to terrestrial rocks, meteorites, and various mineral separates. Terrestrial samples and standards agree within analytical uncertainties but are consistently different from the recommended values of Niederer et al. [F.R. Niederer, D.A. Papanastassiou, G.J. Wasserburg, Geochim. Cosmochim. Acta 45 (1981) 1017] with the largest effect on 50Ti/ 47Ti. The new results provide evidence that the recommended terrestrial 50Ti/ 47Ti is not well constrained; our data are higher by ∼13 ɛ than the recommended value. Better agreement is found with the values recommended by Heydegger et al. [H.R. Heydegger, J.J. Foster, W. Compston, Earth Planet. Sci. Lett. 58 (1982) 406]. Our best estimate for the isotopic composition of terrestrial Ti (relative to 49Ti/ 47Ti = 0.749766) is: 50Ti/ 47Ti = 0.73010, 48Ti/ 47Ti = 10.06884, and 46Ti/ 47Ti = 1.09325. This corresponds to an atomic weight of 47.877, significantly different from the value of 47.867 recommended by IUPAC. A 50Ti/ 47Ti anomaly for bulk Allende of 3.37 ± 0.51 ɛ is found, while for 48Ti/ 47Ti and 46Ti/ 47Ti the data are identical to the terrestrial value within the uncertainties. This is consistent with other recently reported differences between the bulk Earth and chondrites in neutron-rich nuclides.

Reconstruction of Ionization Density Distribution in Hall Thruster Channel from Ion Energy Spectrum of Plasma Jet

Propellant ionization in the Hall thruster discharge channel is a significant process and has strong influence on the thruster's efficiency. In this work, the functional relation has been established between the ionization density distribution and the function of the ion energy distribution through the basic equations governing the ion flow in the Hall thruster channel and the method achieved for reconstructing the ionization density distribution inside the channel by ordinary plasma diagnosis of the potential distribution and ion energy spectrum of the plasma jet. The ionization density distributions of single and double charged ions in an ATON-thruster channel have been reconstructed according to the experimental data of the potential distribution along the axis of the channel and the ion energy spectrum of the plasma jet. The agreement between the calculation and experimental results of the percentage of double charged ions proves the validity of our method achieved in this work.

Variations in the parameters of the erosion lead plasma with distance from the laser target

The main parameters of the erosion lead plasma (the atomic density, the densities of electrons and single-and double-charged ions, the pressure, the mean free path, and the degree of ionization) at distances 1 and 7 mm from the laser target are investigated using emission spectroscopy. The plasma was produced by using a repetitive neodymium laser with a peak intensity of (3–5) × 108 W/cm2, wavelength of 1.06 µm, pulse duration of 20 ns, and repetition rate of 12 Hz.

Electron Detachment Dissociation of Glycosaminoglycan Tetrasaccharides

The first application of electron detachment dissociation (EDD) to carbohydrates is presented. The structural characterization of glycosaminoglycan (GAG) oligosaccharides by mass spectrometry is a longstanding problem because of the lability of these acidic, polysulfated carbohydrates. Doubly-charged negative ions of four GAG tetrasaccharides are examined by EDD, collisionally activated dissociation (CAD), and infrared multiphoton dissociation (IRMPD). EDD is found to produce information-rich mass spectra with both cross ring and glycosidic cleavage product ions. In contrast, most of the product ions produced by CAD and IRMPD result from glycosidic cleavage. EDD shows great potential as a tool for locating the sites of sulfation and other modifications in glycosaminoglycan oligosaccharides.

Influence of Solvent and Counter Ion on Copper Complexes with N-Alkyl-Pyridine-2-Carboxamides as Studied by Electrospray Ionization Mass Spectrometry

The interactions of copper(II) with N-alkyl-pyridine-2-carboxamides (M) were studied by electrospray ionization mass spectrometry. The influence of solvent and counter ion (Cl-, ClO4-) on the type of ions (complexes) observed was discussed. By cone voltage increase, the fragmentation "in source" of the ions discussed was achieved. In methanol solution containing N-alkyl-pyridine-2-carboxamide (M) and CuCl2 the singly- and doubly charged-ions [M+CuCl]+ and [M2+Cu]+2 were detected. In acetonitrile solution containing N-alkyl-pyridine-2-carboxamide and CuCl2, the copper(I)-containing ions [M+CH3CN+Cu]+ were formed. The use of Cu(ClO4)2 instead of CuCl2 resulted in more abundant doubly-charged ions in both methanol and acetonitrlile solutions and, for the former solution, the ions containing methoxyl anion, namely [M+CuOCH3]+, were observed. When water was used as a solvent, the abundant ions corresponding to the protonated ligands were formed, while the ions corresponding to copper complexes were characterised by low abundances.

Modeling of Plasma Flow Around SMART-1 Spacecraft

SMART-1 is the first European spacecraft that uses electric propulsion as the main propulsion system. The thruster characteristics and plasma measurements performed during SMART-1 mission lay a good foundation for understanding spacecraft/plasma interactions. This paper discusses the applications and modifications of spacecraft plasma interaction system software, which originally was developed to simulate an interaction of the space plasma with the spacecraft-surface materials and to compute a plasma-induced charging. The particle-in-cell and Monte Carlo collision (PIC-MCC) method and a simplified and fast approach that tracks only slow ion motion are implemented to model the plasma flow around the spacecraft with electric propulsion. The simplified approach consists of a consecutive application of a direct simulation MC (DSMC)-based software for neutral flow, axisymmetric PIC-MCC for plume flow, and three-dimensional (3-D) PIC software for plasma flow around the spacecraft. Three-dimensional computations are performed to analyze the effects of single- and double-charged Xenon ions, constant and spatially variable electron temperature, an application of quasi-neutral assumption or Poisson solver, and low Earth orbit environment on plasma flow around SMART-1. It was shown that a spatially variable electron temperature has the most significant effect on the plasma-flow properties

The Mycobacterial Thioredoxin Peroxidase Can Act as a One-cysteine Peroxiredoxin

Thioredoxin peroxidase (TPx) has been reported to dominate the defense against H(2)O(2), other hydroperoxides, and peroxynitrite at the expense of thioredoxin (Trx) B and C in Mycobacterium tuberculosis (Mt). By homology, the enzyme has been classified as an atypical 2-C-peroxiredoxin (Prx), with Cys(60) as the "peroxidatic" cysteine (C(P)) forming a complex catalytic center with Cys(93) as the "resolving" cysteine (C(R)). Site-directed mutagenesis confirms Cys(60) to be C(P) and Cys(80) to be catalytically irrelevant. Replacing Cys(93) with serine leads to fast inactivation as seen by conventional activity determination, which is associated with oxidation of Cys(60) to a sulfinic acid derivative. However, in comparative stopped-flow analysis, WT-MtTPx and MtTPx C93S reduce peroxynitrite and react with TrxB and -C similarly fast. Reduction of pre-oxidized WT-MtTPx and MtTPx C93S by MtTrxB is demonstrated by monitoring the redox-dependent tryptophan fluorescence of MtTrxB. Furthermore, MtTPx C93S remains stable for 10 min at a morpholinosydnonimine hydrochloride-generated low flux of peroxynitrite and excess MtTrxB in a dihydrorhodamine oxidation model. Liquid chromatography-tandem mass spectrometry analysis revealed disulfide bridges between Cys(60) and Cys(93) and between Cys(60) and Cys(80) in oxidized WT-MtTPx. Reaction of pre-oxidized WT-MtTPx and MtTPx C93S with MtTrxB C34S or MtTrxC C40S yielded dead-end intermediates in which the Trx mutants are preferentially linked via disulfide bonds to Cys(60) and never to Cys(93) of the TPx. It is concluded that neither Cys(80) nor Cys(93) is required for the catalytic cycle of the peroxidase. Instead, MtTPx can react as a 1-C-Prx with Cys(60) being the site of attack for both the oxidizing and the reducing substrate. The role of Cys(93) is likely to conserve the oxidation equivalents of the sulfenic acid state of C(P) as a disulfide bond to prevent overoxidation of Cys(60) under a restricted supply of reducing substrate.

Sputtered gas-phase dianions detected by high-sensitivity mass spectrometry

The detection of small doubly-charged molecular anions by means of highly sensitive mass spectrometry is discussed. The production of these gas-phase dianions is accomplished by sputtering the specimen with Cs + ions with an energy of a few keV. It is demonstrated that dianions can be detected most easily when the molecular ion has an odd total mass; then, the dianions will show up at half-integral mass numbers in the mass spectrum. In addition, the agreement of the relative abundances of several isotopomers of a dianion with the nominal isotopic pattern corroborates the identification of a dianionic species in the mass spectrum. These features are exemplified by monitoring mixed silicon–oxygen dianions of the general form Si n O 2 n + 1 2 - (with 2 ⩽ n ⩽ 8) in a low-energy mass spectrometer. They were formed by sputtering a silicon wafer at an elevated oxygen partial pressure in the vicinity of the sample’s surface. The flight time through the mass spectrometer of ∼15–30 μs establishes a lower limit with respect to the intrinsic lifetimes of these dianions. Emission energy spectra of various singly- and doubly-charged ions illustrate the occurrence of fragmentation processes. The yields of the doubly- and singly-charged mixed silicon–oxygen anions increase with the ratio of the O 2 arrival rate to the Cs + flux density, but tend to saturate when this ratio approaches unity. The benefits of high-energy accelerator mass spectrometry in dianion detection are illustrated for LiF 3 2 - and CaF 4 2 - .

Surface-induced dissociation and reactions of dications and cations: Collisions of dications C 7H 82+, C 7H 72+, and C 7H 62+ and a comparison with the respective cations C 7D 8[rad]+ and C 7H 7+

Collisions of cations and dications C 7H 8 +/2+, C 7H 7 +/2+, and C 7H 6 2+ generated by electron ionization of toluene with a highly oriented pyrolytic graphite surface were investigated in scattering experiments at the incident energy of 25.3 eV, incident angle of 60° (with respect to the surface normal) and at surface temperatures of 300 and 900 K. The survival probability of ions was rather large, about 10% for the cations and about twice as large for the dications. Only singly-charged ions were observed in the mass spectra of product ions for both singly- and doubly-charged incident ions. In agreement with earlier conclusion of Cooks et al., the primary process in surface collisions of the dications is a single-charge exchange between the approaching dication and the surface at larger distances; hence, the mass spectrum of product ions in fact results from surface interactions of internally excited monocations. This scenario is also supported by measured translational energy distributions and angular distributions of the major product ions which are very similar for both dication- and cation-collisions. Two mechanisms of formation for the fragment ions observed are suggested: either via unimolecular decomposition of the inelastically scattered projectile ion or via decay of the protonated projectile formed by endoergic hydrogen transfer from the surface hydrocarbons to the projectile ion. The translational energy distributions of ions originating from dissociation of the surface-excited projectile ions peak at higher energies than those of the ions resulting from decomposition of surface-protonated precursor ions.

Ion acceleration in vacuum arc cathode plasma jets with large rates of current rise

A model of plasma acceleration in a high-current short pulse vacuum arc was developed. The mathematical description includes equations for the cathode spot and the plasma jet, which were solved for rates of current rise dI/dt in the range of 0.01-10 GA/s. The multicharged ions in the cathode spot were taken in account. It was shown that the plasma could be accelerated to the measured energy by a gasdynamic mechanism. The ion energy, cathode erosion rate, and the ratio of the ion flux to the electron flux are linked by the equations. The calculated cathode erosion rate varies from 200 to 10 /spl mu/g/C when the ion energy increases from 0.1 to 10 keV. The ion current to the cathode mainly consists of singly- and doubly-charged ions. The singly-charged ion current fraction decreases with spot current decreasing and rate of current rise increasing.

Differentiation of ionised benzimidazole from its isomeric alpha-distonic ion by collision-induced dissociation and neutralisation-reionisation mass spectrometry.

Ionised benzimidazole and its isomeric alpha-distonic ion (or ionised ylid) have been examined by recording their metastable ion, collision-induced dissociation and neutralisation-reionisation mass spectra. These tautomers may be distinguished by careful consideration of key features of the collision-induced dissociation spectra, with or without prior neutralisation and reionisation. Formation of doubly-charged ions by charge stripping occurs preferentially when the alpha-distonic ion is subjected to collision. This alpha-distonic ion survives neutralisation and reionisation, thus establishing that the corresponding ylid is stable on the microsecond time frame. The effects of benzannulation on the ease of differentiation of classical and distonic radical cations derived from biologically important heterocycles are considered.

Peptide photodissociation at 157 nm in a linear ion trap mass spectrometer

The photodissociation by 157 nm light of singly- and doubly-charged peptide ions containing C- or N-terminal arginine residues was studied in a linear ion trap mass spectrometer. Singly-charged peptides yielded primarily x- and a-type ions, depending on the location of the arginine residue, along with some related side-chain fragments. These results are consistent with our previous work using a tandem time-of-flight (TOF) instrument with a vacuum matrix-assisted laser desorption/ionization (MALDI) source. Thus, the different internal energies of precursor ions in the two experiments seem to have little effect on their photofragmentation. For doubly-charged peptides, the dominant fragments observed in both photodissociation and collisionally induced dissociation (CID) experiments are b- and y-type ions. Preliminary experiments demonstrating fragmentation of multiply-charged ubiquitin ions by 157 nm photodissociation are also presented.

Active Kinase Proteome Screening Reveals Novel Signal Complexity in Cardiomyopathy

Recent advances in the characterization of the phosphoproteome have been limited to measuring phosphorylation statuses, which imply but do not measure protein kinase activity directly. As such, the ability to screen, compare, and define multiple protein enzymatic activities across divergent samples remains a daunting challenge in proteomics. Here, we describe a gel-based kinase assay coupled to MS identification as an approach to map global kinase activity and assign pathway architecture to specified biologic contexts. We demonstrate the utility of this method as a platform for the comparison of proteomes based on differences in both kinase activities and for use in the de novo substrate identification for individual kinases. This approach allowed us to map the signal perturbations in the post-natal heart that were associated with activation of a myopathic cascade as mediated by the mitogen-activated protein kinase MKK6 and established the novel observation that MKK6 promotes the development of cardiomyopathy through multiple substrate interactions.

Prediction and modelling of doubly-charged ions in the Earth's upper atmosphere

Abstract. We discuss the existence of the doubly-charged ions N2++, O2++ and O++ in the Earth's ionosphere through the theoretical computation of density profiles over the altitude range 100-500km calculated with the TRANSCAR model. Photoproductions and electron impact productions are described in detail. The photochemical equilibrium assumption verified in this context yields density profiles, validated by comparison to the measurements of the satellite Atmosphere Explorer. Those three dications are lost essentially by dissociative recombination and collisions with the neutrals N2, O2 and O. The metastable lifetime of N2++ is 3s and is estimated at 4s for O2++. A survey of the sensitivity to geophysical parameters (solar activity, latitude and solar zenith angle) is also shown. Emphasis is cast on the need for rate constants for chemical reactions involving doubly-charged ions. The fit of the model yields an estimated value of 1.06±0.40x10-10cm3s-1 for the rate constant of the O+++O reaction.

Pyridine N‐oxide and pyridine‐d5N‐oxide: an electrospray/tandem mass spectrometric study carried out at high mass resolution

A mass spectrometric study of pyridine N-oxide and pyridine-d5 N-oxide was carried out with a hybrid quadrupole/time-of-flight (TOF) mass spectrometer coupled with an electrospray (ES) source. In addition to the observation of protonated, sodiated, and proton-bound dimers of pyridine N-oxide and pyridine-d5 N-oxide, mass scans revealed the presence of several doubly-charged ion species. Doubly-charged ions of m/z 191 were identified as diprotonated tetramers of pyridine N-oxide; a structure has been proposed for the diprotonated tetramer and its energy relative to that of protonated pyridine N-oxide has been obtained from geometry optimizations. The principal ion species observed were subjected to collision-induced dissociation; accurate mass measurements were made of each fragment ion so as to determine its elemental composition. On the basis of mass spectrometric evidence, it is suggested that dissociation of pyridine N-oxide may occur during the ES process and the resulting fragments become embedded in doubly-charged ions. The proton affinity for both pyridine N-oxide and pyridine-d5 N-oxide was calculated; the difference between these proton affinities was compared with an experimentally determined difference between the proton affinities of pyridine N-oxide and pyridine-d5 N-oxide.