Charged Parent Ions Research Articles

Determination of tetrabromobisphenol A and its brominated derivatives in water, sediment and soil by high performance liquid chromatography-tandem mass spectrometry.

Tetrabromobisphenol A (TBBPA) was typical brominated flame retardant and potential environmental endocrine disruptor, and it had persistence, bioaccumulation and chronic toxicity. Simultaneous determination of ultra-trace TBBPA, tribromobiphenol A (tri-BBPA), dibromobiphenol A (di-BBPA), monobromobisphenol A (mono-BBPA) and bisphenol A (BPA) was developed by high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS), the parent ion charge ratios (m/z) had been optimized. The linear range was wider and the limit of detection was (LOD) 0.09 ~ 0.21ngmL-1, which could detect trace pollutants. The extraction efficiency was improved by optimizing the parameters, HLB cartridge was used in the water sample by solid phase extraction (SPE), the recovery rates in water samples were over 80.28% with three concentration levels, the relative standard deviations (RSD) were less than 7.12%, and the minimum detection limit of the method was 0.90 ~ 2.10 × 10-3ngmL-1. Soil and sediment samples were extracted by accelerated solvent extraction (ASE), the recovery rates in soil and sediment were over 79.40% and 75.65%, the minimum detection limit was 0.0225 ~ 0.0525ngg-1, RSD was less than 7.19%. The proffered method was successfully utilized to detect actual samples, the residue of di-BBPA and mono-BBPA are detected in Naihe River and Shuxi River in Tai'an City, residue of di-BBPA and mono-BBPA was detected in the soil, and there was low residual amount of di-BBPA, mono-BBPA and BPA in the sediment of Shuxi River.

Cold-target electron-ion-coincidence momentum-spectroscopy study of electron-impact single and double ionization of N2 and O2 molecules

We report experimental studies of electron-impact ionization of nitrogen (${\mathrm{N}}_{2}$) and oxygen (${\mathrm{O}}_{2}$) molecules using a cold target recoil ion momentum spectrometer (COLTRIMS, reaction microscope). The recoil ion is detected in coincidence with one outgoing electron such that the momentum vectors and consequently the kinetic energies for these final-state particles are determined. The ionization cross sections for producing the doubly and singly charged parent ions were measured as a function of the incident electron energy ranging from 50 to 600 eV. For molecular dications, e.g., ${\mathrm{O}}_{2}^{2+}$, the cross sections are obtained by measuring both the ion time of flight and two-dimensional position spectra, which is demonstrated to be an efficient way to suppress the contribution of the dissociation channels with the ${\mathrm{O}}^{+}$ products as both ions have the identical mass-to-charge ratios. The projectile energy-loss spectra correlated to the final-state ions are obtained, which provide direct evidence of the ionization mechanisms of ${\mathrm{N}}_{2}$ and ${\mathrm{O}}_{2}$ molecules. It is found that the ${\mathrm{O}}_{2}^{2+}$ dication is produced mainly by Auger process after single ionization in $2{\ensuremath{\sigma}}_{g}$ inner-valence shell of ${\mathrm{O}}_{2}$ molecule, while the ${\mathrm{N}}_{2}^{2+}$ dication is generated by the direct removal of two electrons from the outermost $3{\ensuremath{\sigma}}_{g}$ orbital of ${\mathrm{N}}_{2}$ molecule.

Imaging the Dynamics of the Electron Ionization of C2F6

The dissociation of C2F6 following electron ionization at 100 eV has been studied using multimass velocity-map ion imaging and covariance-map imaging analysis. Single ionization events form parent C2F6+ cations in an ensemble of electronic states, which follow a multiplex of relaxation pathways to eventually dissociate into ionic and neutral fragment products. We observe CF3+, CF2+, CF+, C+, F+, C2F5+, C2F4+, C2F2+, and C2F+ ions, all of which can reasonably be formed from singly charged parent ions. Dissociation along the C–C bond typically forms slow-moving, internally excited products, whereas C–F bond cleavage is rapid and impulsive. Dissociation from the à state of the cation preferentially forms C2F5+ and neutral F along a purely repulsive surface. No other electronic state of the ion will form this product pair at the electron energies studied in this work, nor do we observe any crossing onto this surface from higher-lying states of the parent ion. Multiply charged dissociative pathways are also explored, and we note characteristic high kinetic energy release channels due to Coulombic repulsion between charged fragments. The most abundant ion pair we observe is (CF2+, CF+), and we also observe ion pair signals in the covariance maps associated with almost all possible C–C bond cleavage products as well as between F+ and each of CF3+, CF2+, CF+, and C+. No covariance between F+ and C2F5+ is observed, implying that any C2F5+ formed with F+ is unstable and undergoes secondary fragmentation. Dissociation of multiply charged parent ions occurs via a number of mechanisms, details of which are revealed by recoil-frame covariance-map imaging.

Comparison of the double-photoionization processes in triphenylene and corannulene with coronene

We have studied the production of doubly charged molecular ions by a single photon for the aromatic molecules triphenylene (C18H12) and corannulene (C20H10) using monochromatized synchrotron radiation from 18 eV to 270 eV. We compare our results with previously published data for partially deuterated benzene (C6H3D3), pyrene (C16H10), and coronene (C24H12). The question that we address in this paper is how the different but similar molecular structures of coronene, corannulene, and triphenylene affect the photon-energy dependence of the ratio of doubly to singly charged parent ions. A theoretical analysis of the main features in terms of independent molecular subsystems will be discussed.

Ionization and fragmentation of fluorene upon 250 keV proton impact

We have investigated the ionization and fragmentation of a polycyclic aromatic hydrocarbon molecule, fluorene ( $$\hbox {C}_{{13}}\,\hbox {H}_{{10}}$$ ), upon proton impact with energy 250 keV. Various ionization and fragmentation products have been identified. Hydrogen-loss process from singly and doubly ionized parent molecules has been found to be a dominating channel. In case of singly ionized molecule, up to three H-losses have been observed. However, two H-loss ion has not been observed. For the doubly ionized molecule up to four H-losses have been observed. The ratio of doubly to singly charged parent ions are found to be quite high compared to the atomic targets, such as, He and Ne.

Coulomb explosion imaging for gas-phase molecular structure determination: An ab initio trajectory simulation study.

Coulomb explosion velocity-map imaging is a new and potentially universal probe for gas-phase chemical dynamics studies, capable of yielding direct information on (time-evolving) molecular structure. The approach relies on a detailed understanding of the mapping between the initial atomic positions within the molecular structure of interest and the final velocities of the fragments formed via Coulomb explosion. Comprehensive on-the-fly ab initio trajectory studies of the Coulomb explosion dynamics are presented for two prototypical small molecules, formyl chloride and cis-1,2-dichloroethene, in order to explore conditions under which reliable structural information can be extracted from fragment velocity-map images. It is shown that for low parent ion charge states, the mapping from initial atomic positions to final fragment velocities is complex and very sensitive to the parent ion charge state as well as many other experimental and simulation parameters. For high-charge states, however, the mapping is much more straightforward and dominated by Coulombic interactions (moderated, if appropriate, by the requirements of overall spin conservation). This study proposes minimum requirements for the high-charge regime, highlights the need to work in this regime in order to obtain robust structural information from fragment velocity-map images, and suggests how quantitative structural information may be extracted from experimental data.

Covariance-map imaging study into the fragmentation dynamics of multiply charged CF3I formed in electron-molecule collisions

We have previously presented a comprehensive velocity-map imaging study into the dissociative electron-ionisation dynamics of CFI at energies ranging from 20 to 100 eV, focusing on dissociation channels of singly charged parent ions. Here we extend this work to include channels arising from doubly and triply charged CFI ions formed in collisions with 40–100 eV electrons. Both the dication and trication can dissociate either via two-body Coulomb explosion to form CF + I/I, or via a variety of many-body dissociation channels involving the loss of one or more neutral fluorine atoms. Covariance mapping of the charged fragments allows us to distinguish between the various possible dissociation mechanisms that could account for these products.

Proteome Based de novo Sequencing of Novel Conotoxins from Marine Molluscivorous Cone Snail Conus amadis and Neurological Activities of Its Natural Venom in Zebrafish Model.

Conus amadis is a carnivorous snail found abundantly in coastal waters of India. Despite its abundance in southern coastal waters of India and the fact that most of the conotoxin act in neuronal system, research work on Conus amadis venom was not much focused. So we have made a brief study on the venom complex of Conus amadis to identify the library of novel conotoxins and to screen the natural venom for neurological function. De novo sequencing of novel conopeptides from the venom cocktail of Conus amadis and to screen its natural venom for the presence of biological activities in zebrafish model. Proteome based MALDI-TOF and LC-MS-MS analysis for identification of novel conotoxins and subsequent sequencing. Due to the complex disulfide rich nature of the venom peptides, the study also involves global chemical modification experiments of the venom extract to unambiguously determine the sequence of novel conotoxins. Biological function analysis of natural venom was tested in zebrafish model to ascertain anti-epileptic properties. In this study, we have identified 19 novel conotoxins containing 1, 2 & 3 disulfides, belonging to different classes. Among them, 2 novel contryphans, 3 T-superfamily conotoxins, 2 A-superfamily conotoxins and 2 Mini M-Superfamily conotoxins were sequenced to its amino acid level from the fragmented spectrum of singly and doubly charged parent ions using de novo sequencing strategies. ama1054, a contryphan peptide toxin, possesses post translationally modified bromo tryptophan at its seventh position. Except ama1251, all the sequenced peptide toxins possess modified C-terminal amidation. Crude venom exhibited anticonvulsant properties in pentylenetetrazole-induced seizure in zebrafish larvae, which suggested anti-epileptic property of the venom cocktail. Acetylcholinesterase activity was also identified in the venom complex. Based on the preliminary evidence, if this study is extended further through bioassay guided purification, could possibly yield peptide toxins with anticonvulsant and other neurologically active molecules.

Analysis of multiply charged monomers and dimers of human islet amyloid polypeptide by collision-induced dissociation with electrospray ionization mass spectrometry

Collision-induced dissociation (CID) with ESI-MS was used to obtain structural information on early-stage aggregation of hIAPP (human islet amyloid polypeptide) monomers and oligomers. MS analysis showed that the hIAPP monomers and oligomers were multiply charged. MS/MS analysis indicated that the hIAPP monomers adopt different structures depending on the parent ion charge state. The fragmentation patterns indicated structural similarity of M2+ & M3+ and M4+ & M5+ (M = monomer). MS/MS analysis of the dimers showed that D5+ (D = dimer) comprised M2+ and M3+ subunits, and the peptide bond dissociated in the 15–37 residue region of the monomer subunit.

Fragmentation of C2H2 2+ in collisions with 100 eV electrons

The fragmentation of C2H2 2+ dications following 100 eV electron impact double ionization of acetylene was studied experimentally using a cold target recoil-ion momentum spectroscopy. A weak extraction field was adopted to increase the experimental resolution. Meanwhile, as a consequence of the large momentum generated by the Coulomb repulsive force, the particles which have similar charge to mass ratio such as C+ and CH+ cannot be distinguished directly from the time of flight. In order to obtain a comprehensive understanding of the experimental results, a Monte Carlo (M-C) method was used to simulate the time of flight under experimental conditions. With the help of the M-C method, four reaction channels, the Coulomb explosion of the doubly charged parent ions C2H2 2+ into the fragment ions CH+ + CH+,C+ + CH+2, C+ + CH+, C+ + C+, were simulated and the kinetic energy release (KER) distributions were deduced. In particular, the structure of fragmentation channel to C+ + CH+ represents a typical feature of the absence of hydrogen migration, which was not observed in previous studies. The KER in the fragmentation reaction of C2H2 2+ has been used to obtain precursor state energy for the formation of product ion pairs. In general, good agreement was achieved between our KER results and available experimental data in previous works.

Formation, stability and dissociation dynamics of cations (n = 1 − 2) in 3.5 keV e−-N2 collisions studied using the energy resolved electron–ion coincidence technique

Coincidences between energy selected electrons and ions produced in the decay of a core hole ionized (excited) state in a free nitrogen molecule have been measured at three specified energies of emitted electrons to reveal the individual pathways produced in 3.5 keV electron-induced fragmentation processes. From these measurements, it has been possible to show, for the first time, that in addition to the normal Auger decay, the resonant Auger excitation channels also share their appreciable contributions in producing singly charged parent ions in an electron-induced collision system. The correlations between ion fragmentation products and electronic structures with a hole configuration in singly-, doubly- and possibly in triply charged molecular electronic states populated in the electronic decay of the initial core hole have been studied and discussed. KER values obtained from our experiments are found to be consistent with the previous results of photo absorption experiments for fragmentation channel → N+ + N+; however, N2+ fragment ions are found to arise mainly from the fragmentation channel → N2+ + N and to possess relatively low kinetic energies in the considered region of binding energies.

Doubly and Triply Charged Species Formed from Chlorobenzene Reveal Unusual C-Cl Multiple Bonding.

In free-radical halogenation of aromatics, singly charged ions are usually formed as intermediates. These stable species can be easily observed by time-of-flight mass spectrometry (TOF-MS). Here we used electron and proton beams to ionize chlorobenzene (C6H5Cl) and investigate the ions stability by TOF-MS. Additionally to the singly charged parent ion and its fragments, we find a significant yield of doubly and triply charged parent ions not previously reported. In order to characterize these species, we used high-level theoretical methods based on density functional theory (DFT), coupled-cluster (CC), and generalized valence bond (GVB) to calculate the structure, relative stabilities, and bonding of these dications and trications. The most stable isomers exhibit unusual carbon-chlorine multiple bonding: a terminal C═Cl double bond in a formyl-like CHCl moiety (1, rC-Cl = 1.621 Å) and a ketene-like C═C═Cl cumulated species (2, rC-Cl = 1.542 Å). The calculations suggest that an excited state of 2 has a nitrile-like C≡Cl triple bond structure.

Femtosecond Laser Mass Spectrometry and High Harmonic Spectroscopy of Xylene Isomers

Structural isomers, molecules having the same chemical formula but with atoms bonded in different order, are hard to identify using conventional spectroscopy and mass spectrometry. They exhibit virtually indistinguishable mass spectra when ionized by electrons. Laser mass spectrometry based on photoionization of the isomers has emerged as a promising alternative but requires shaped ultrafast laser pulses. Here we use transform limited femtosecond pulses to distinguish the isomers using two methods. First, we probe doubly charged parent ions with circularly polarized light. We show that the yield of doubly charged ortho-xylene decreases while para-xylene increases over a range of laser intensities when the laser polarization is changed from linear to circular. Second, we probe high harmonic generation from randomly oriented isomer molecules subjected to an intense laser field. We show that the yield of high-order harmonics varies with the positioning of the methyl group in xylene isomers (ortho-, para- and meta-) and is due to differences in the strength of tunnel ionization and the overlap between the angular peaks of ionization and photo-recombination.

Multielectron Effects in the Strong Field Sequential Ionization of Aligned CH3I Molecules.

Strong field sequential ionization of symmetric-top CH3I molecules is studied experimentally by using a combined method of femtosecond laser-induced impulsive alignment and time-of-flight mass spectrometry. Both alignment- and angular-dependent ion yields have been measured, and the sequential ionization of a multielectron has been discussed. It is found that the maximum ionization occurs when the polarization of probe laser is perpendicular to the internuclear axis of molecules, and the signal of fragment ion peaks at the polarization of the probe laser is parallel to the internuclear axis of molecules. The angular distribution of ions indicated that ionization of π-type orbitals corresponds to generation of charged parent ions and ionization of σ-type orbitals corresponds to generation of fragment ions. The sequential release of multielectrons for Coulomb explosion channels is studied by analysis of the time evolutions of multicharged In+ (n = 1-4) signals.

The Role of Super-Atom Molecular Orbitals in Doped Fullerenes in a Femtosecond Intense Laser Field

SynopsisThe photoionization of complex targets, such as endohedral fullerenes, in strong laser fields has been studied experimentally and theoretically. We used the prototype Ho3N@C80 interacting with intense (0.1-5×1014 W/cm2), short (30 fs), 800 nm laser pulses giving rise to multiply charged parent ions. The power law dependence of Ho3N@C80q+, q=1-2, was found to be different from that of C60. Time-dependent density functional theory computations suggest that the fast ionization of the SAMO states in Ho3N@C80 is responsible for the different power law behavior.

Ultrafast proton migration and Coulomb explosion of methyl chloride in intense laser fields

We investigated the ultrafast proton migration and the Coulomb explosion (CE) dynamics of methyl chloride (CH3Cl) in intense femtosecond laser fields at the wavelengths of 800 nm (5.5 × 1014 W/cm2) and 400 nm (4 × 1014 W/cm2), respectively. Various fragment channels from molecular dication and trication were observed by coincidence momentum imaging through the measurement of their kinetic energy releases (KERs). The proton migration from different charged parent ions was analyzed from the obtained KER distributions. For the direct CE channel of CH3+ + Cl+ and CH3+ + Cl2+, the contribution of multiply excited electronic states and multicharged states is identified. In addition, the measurements of relative yields of the fragmentation channel at different laser wavelengths provide a selective control of proton migration for CH3Cl molecules in intense laser fields.

Double photoionization of tropone and cyclooctatetraene.

We have studied the double-photoionization process of tropone (C7H6O) and cyclooctatetraene (C8H8) as a function of photon energy using monochromatized synchrotron radiation between 18 and 270 eV. We compare our results with previously published data for partially deuterated benzene (C6H3D3), which exhibits three distinct features in the ratio of doubly to singly charged parent ions, whereas pyrrole (C4H4N) exhibits only two of these features. The question that we address in this paper is how molecules with different molecular structures (pentagonal, hexagonal, heptagonal, and octagonal carbon rings) affect the photon-energy dependence of this ratio.

Double photoionization of tribromoborazine from 25 to 138 eV

We have measured the yield for the photoproduction of singly and doubly charged parent ions of the inorganic molecule tribromoborazine [(BrBNH)${}_{3}]$, a molecule in which three bromine atoms replace three hydrogen atoms in borazine [(BH)${}_{3}$(NH)${}_{3}]$. Borazine is isoelectronic and isostructural to benzene. We compare the ratio of doubly to singly charged parent ions as a function of the photon energy to the ratio for benzene. We find similarities but also marked differences between the two molecules. The first double-ionization threshold was found to be at 28.5(4) eV.

Double photoionization of halogenated benzene

We have experimentally investigated the double-photoionization process in C6BrF5 using monochromatized synchrotron radiation. We compare our results with previously published data for partially deuterated benzene (C6H3D3) over a wide range of photon energies from threshold to 270 eV. A broad resonance in the ratio of doubly to singly charged parent ions at about 65 eV appears shifted in energy compared to benzene data. This shift is due to the difference in the bond lengths in two molecules. A simple model can explain the shape of this resonance. At higher photon energies, we observe another broad resonance that can be explained as a second harmonic of the first resonance.

Photofragmentation Mechanisms of Chlorosulfonyl Isocyanate, ClSO2NCO, Excited with Synchrotron Radiation between 12 and 550 eV.

The unimolecular photofragmentation mechanisms of chlorosulfonyl isocyanate, ClSO2NCO, excited with tunable synchrotron radiation between 12 and 550 eV, were investigated by means of time-of-flight (TOF) coincidence techniques. The main fragmentation mechanism after single ionization, produced by irradiation of an effusive beam of the sample with synchrotron light in the valence electron region, occurs through the breaking of the Cl-S single bond, giving a chloride radical and a SO2NCO(+) fragment. This mechanism contrasts with the one observed for the related FSO2NCO, in which the rupture of the S-N bond originates the FSO2(+) fragment. The energies of the shallow- (S 2p, Cl 2p, and S 2s) and core-shell (C 1s, N 1s, and O 1s) electrons were determined by X-ray absorption. Transitions between these shallow and core electrons to unoccupied molecular orbitals were also observed in the total ion yield (TIY) spectra. Fourteen different fragmentation mechanisms of the doubly charged parent ion, ClSO2NCO(2+), were inferred from the bidimensional photoelectron-photoion-photoion-coincidence (PEPIPICO) spectra. The rupture of the S-N bond can evolve to form NCO(+)/SO2(•+), NCO(+)/SO(•+), or S(•+)/NCO(+) pairs of ions. The Cl-S bond breaking originates different mechanisms, Cl(+)/SO(•+), Cl(+)/S(•+), CO(•+)/S(•+), O(•+)/SO(•+), O(•+)/Cl(+), O(•+)/S(•+), C(•+)/S(•+), and C(•+)/O(•+) pairs being detected in coincidence as the final species. Another three coincidence islands can only be explained with an initial atomic rearrangement forming ClNCO(2+), ONCO(2+), and ClCO(2+), as precursors of CO(•+)/Cl(+), O(•+)/CO(•+), and C(•+)/Cl(+) pairs, respectively. The formation of Cl(•) radical is deduced from several mechanisms.