Ion Branching Research Articles

Rapid Removal of Cr(VI) from Wastewater by Surface Ionized Iron-Based MOF: Ion Branching and Domain-Limiting Effects

Exploring the ratio of metal centers to organic ligands and the amount of DMF are important to improve the stability and adsorption efficiency of MOF materials as adsorbents. In this work, MIL101(Fe)-Na2CO3 was successfully obtained by modification with formic acid, sodium carbonate, carbon nanotubes, and moieties. The adsorption efficiency of MIL-101(Fe) on Cr(VI) was greatly improved, and the removal efficiency was able to reach 100% in 20 min with a maximum adsorption capacity of 20 mg/g. The inhibition order of the competing anions for the removal of hexavalent chromium was as follows: Cl− < NO3− < SO42−. The analysis of the adsorption thermodynamic model found that the adsorption of MIL101(Fe)-Na2CO3 for Cr(VI) showed spontaneous heat-absorbing and entropy-increasing chemisorption behavior. When using NaOH as the eluent and HCl as the regeneration stabilizer, MIL-101(Fe)-Na2CO3 had good adsorption capacity in multiple cycles.

Electron scattering with ethane adsorbed on rare gas multilayers: Hole transfer, coulomb decay, and ion dissociation.

Positive ion desorption following electron impact dissociative ionization of ethane adsorbed on Ar, Kr, and Xe multilayers has been studied as a function of incident electron energy from threshold to 100eV. Based on the dependence of ion yields on the identity of the rare gas, it is likely that the majority of ethane molecules undergo indirect ionization following hole transfer from the ionized underlying rare gas. This has also been corroborated by density of states calculations showing the energetic alignment of the outer valence states of ethane and the condensed rare gas ionization energies. Due to the near-resonant nature of charge transfer for single-hole states, the ethane molecular ion is excited to different final ionic states on different rare gases, which leads to differences in ion desorption yields and branching ratios. The quantitative yields increase with increasing ionization energy gap between the rare gas and ethane, in the order Ar > Kr > Xe. The large increase in yields from 25eV onwards for all rare gases is likely due to the formation and decay of two-hole states on neighboring rare gas and ethane molecules due to interatomic and intermolecular Coulomb decay (ICD) and not electron transfer mediated decay (ETMD). The ICD and ETMD pathways become accessible when the incoming electron has sufficient energy to excite the inner valence ns level of the rare gas to a Rydberg state or ionize it. The experimental findings are supported by calculations of thresholds, density of states for the final configurations of these processes, and coupling strengths for hole transfer between ethane and rare gases. The fragment ion branching ratios vary with energy from threshold to about 35eV, showing the fragmentation pattern changes with the mode of hole transfer and availability of excess energy. Sigma C-C bonds are more likely to break than C-H bonds in the mid-20eV range, and this effect is most pronounced for Xe, followed by Kr, and then Ar.

Investigation of several halogenated organic compounds reacting with O2+• using selective reagent ion-time-of-flight-mass spectrometry

Halogenated organic compounds represent an important group of chemicals that have found use in a wide array of research, medical and industrial applications. This raises the question as to which analytical techniques are most suitable for detecting and monitoring in real-time these compounds in the environment. To provide underpinning information on the potential use of chemical ionisation mass spectrometric techniques, we present here details of a selective reagent ion-time-of-flight-mass spectrometry (SRI-ToF-MS) fundamental study characterising the reactions of O2+• with six common halogenated organic compounds, namely, 2,2,2-trifluoroethanol (TFE, CF3CH2OH), 1,1,1,-trifluoroacetone (TFA, CH3COCF3), 1,1,2,2-tetrafluoro-3-methoxypropane (TMP, CHF2CF2CH2OCH3), 1,1,1,3,3,3-hexafluoro-2-methoxypropane (isoflurothyl, (CF3)2–CHO–CH3)), 2-chloro-1,1,2-trifluoro-1-methoxyethane (CTME, CH3OCF2CHFCl) and 1-ethoxy-1,1,2,2-tetrafluoroethane (ETE, CH3CH2OCF2CHF2). We investigated the distributions of the product ions as a function of the reduced electric field strength (E/N) between 65 Td and 205 Td. Five of the halogenated organic compounds generated rather simple product ion distributions. Only one, non-halogenated product ion resulted from each of the reactions of O2+• with TFE (CH2OH+), TFA (CH3CO+) and TMP (CH3OCH2+). For the other two out of the first five compounds, isoflurothyl and CTME, three product ions were observed, but only one of these was dominant with a product ion branching percentage of ∼80% throughout the reduced electric field range investigated: C3H4F3O+ resulting from isoflurothyl and C2H3F2O+ from CTME. The sixth compound, ETE, displayed a much richer reaction ion chemistry than the other five compounds. A total of eight product ions were identified, two of which dominated over most of the investigated E/N range, namely C4H5F4O+ and C2H5+. The potential chemical pathways that lead to the formation of the major and minor observed product ions are discussed for all six compounds. We show that SRI-ToF-MS is a useful technique to study the reactions of halogenated organic compounds with O2+•. Its potential use for monitoring TFE, TFA and TMP is limited because the single product ion observed for each of these volatiles is not sufficiently specific and thus characteristic to the originating compound (i.e., reactions of O2+• with non-halogenated organic compounds will also result in the same product ions). However, SRI-ToF-MS could be considered as a potential analytical tool to detect and monitor isoflurothyl, CTME and ETE, as the fluorinated product ions resulting from their reactions with O2+• allow for their detection with a high level of analytical confidence.

Accurate selected ion flow tube mass spectrometry quantification of ethylene oxide contamination in the presence of acetaldehyde.

In September 2020, traces of ethylene oxide (a toxic substance used as a pesticide in developing countries but banned for use on food items within the European Union) were found in foodstuffs containing ingredients derived from imported sesame seed products. Vast numbers of foodstuffs were recalled across Europe due to this contamination, leading to expensive market losses and extensive trace exposure of ethylene oxide to consumers. Therefore, a rapid analysis method is needed to ensure food safety by high-throughput screening for ethylene oxide contamination. Selected ion flow tube mass spectrometry (SIFT-MS) is a suitable method for rapid quantification of trace amounts of vapours in the headspace of food samples. It turns out, however, that the presence of acetaldehyde complicates SIFT-MS analyses of its isomer ethylene oxide. It was proposed that a combination of the H3O+ and NO+ reagent ions can be used to analyse ethylene oxide in the presence of acetaldehyde. This method is, however, not robust because of the product ion overlaps and potential interferences from other matrix species. Thus, we studied the kinetics of the reactions of the H3O+, NO+, OH- and O-˙ ions with these two compounds and obtained their rate coefficients and product ion branching ratios. Interpretation of these experimental data revealed that the OH- anions are the most suitable SIFT-MS reagents because the product ions of their reactions with acetaldehyde (CH2CHO- at m/z 43) and ethylene oxide (C2H3O2- at m/z 59) do not overlap.

A SIFT-MS study of positive and negative ion chemistry of the ortho-, meta- and para-isomers of cymene, cresol, and ethylphenol.

Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) is a soft ionisation technique based on gas phase ion-molecule reaction kinetics for the quantification of trace amounts of volatile organic compound vapours. One of its previous limitations is difficulty in resolving isomers, although this can now be overcome using different reactivities of several available reagent cations and anions (H3O+, NO+, O2+˙, O-˙, OH-, O2-˙, NO2-, NO3-). Thus, the ion-molecule reactions of these eight ions with all isomers of the aromatic compounds cymene, cresol and ethylphenol were studied to explore the possibility of their immediate identification and quantification without chromatographic separation. Rate coefficients and product ion branching ratios determined experimentally for the 72 reactions are reported. DFT calculations of their energetics confirmed the feasibility of the suggested reaction pathways. All positive ion reactions proceeded fast but largely did not discriminate between the isomers. The reactivity of the anions was much more varied. In all cases, OH- reacts by proton transfer forming (M-H); NO2- and NO3- were unreactive. The differences observed for product ion branching ratios can be used to identify isomers approximately.

Advances in Magnum-PSI probe diagnosis in support of plasma–surface interaction studies

Magnum-PSI is a linear plasma generator equipped with a superconducting magnet, assuring fusion devices relevant conditions at plasma–surface interface. The plasma column was diagnosed using 64 probes embedded in the target. The cross-sectional distributions of plasma parameters (floating potential, ion saturation current and electron temperature) were measured for hydrogen and deuterium plasmas under various discharge conditions. The radial profile of the floating potential across the plasma column can be described by a reversed Mexican hat-like wavelet, having the most negative potential at the center of the plasma column. The negativity of the floating potential diminishes when the discharge current increases or the magnetic field decreases. The axial gradient of the floating potential is reduced by increasing the magnetic field. The ion saturation current is maximum at the center of the plasma column, increasing with both the discharge current and magnetic field. The ion flux to the target, estimated from Thomson scattering (TS) data, was confirmed by probe measurements. The electron temperature estimated from the ion branch of the probe current–voltage characteristic is few times larger than that obtained from TS. By increasing the gas pressure in the target chamber, the time-dependent ion saturation current measured by probes changes from a constant average current (when the plasma column is attached to the target) to a fluctuating average current with scattered peaks (in a partially detached regime) which vanishes completely in the fully detached regime. With respect to hydrogen, the plasma column is wider in deuterium and is characterized by less negative floating potential distributions.

Selected Ion Flow Tube – Mass Spectrometry (SIFT-MS) study of the reactions of H3O+, NO+ and O2+ with a range of oxygenated volatile organic carbons (OVOCs)

Selected Ion Flow Tube-Mass Spectrometry (SIFT-MS) uses soft chemical ionisation, typically by H3O+, NO+ and O2+, to analyse trace gases in real time at mixing ratios down to low parts per trillion by volume (pptv) and has recently been demonstrated as an effective method for monitoring volatile organic compounds (VOCs) in the atmosphere. SIFT-MS analysis requires accurate rate coefficient and product ion branching ratio data to allow for accurate mixing ratio calculations without the need for calibration standards. Most rate constant data have been measured using helium as the carrier gas. Here we report rate constants of a number of oxygenated volatile organic compounds (OVOCs) alongside benzene for H3O+, NO+ and O2+ reagent ions in nitrogen carrier gas, using a permeation tube calibration source and a certified gas standard to introduce known concentrations into the SIFT-MS. This includes the first reported literature rate constant for nonanal using SIFT-MS. We found that the rate constants for most compounds measured in nitrogen carrier gas were similar to those measured in helium. However, the NO+ rate constants for ketones measured in nitrogen were 1.2–5 times lower than those measured in helium. We observe higher fragmentation due to changes made to the lens voltages of the instrument in order to tune for higher sensitivity, altering the reagent ion energies. We also show the impact of increasing the flow tube temperature and voltage on the sensitivity and ionisation of benzene, butanone and butanal under both dry and humid conditions. Some of the SIFT-MS compound library entries are data from historic SIFT-MS instruments that lacked a heated flow tube, and therefore suffered from higher water clustering than current commercial SIFT-MS models. We show that a higher flow tube temperature reduces the amount of water adduct formation thereby simplifying compound concentration determination. These results demonstrate the need to ensure that the library data used are acquired under the same conditions as the experiment being performed.

Kinetics of reactions of NH4 + with some biogenic organic molecules and monoterpenes in helium and nitrogen carrier gases: A potential reagent ion for selected ion flow tube mass spectrometry.

To assess the suitability of NH4 + as a reagent ion for trace gas analysis by selected ion flow tube mass spectrometry, SIFT-MS, its ion chemistry must be understood. Thus, rate coefficients and product ions for its reactions with typical biogenic molecules and monoterpenes need to be experimentally determined in both helium, He, and nitrogen, N2 , carrier gases. NH4 + and H3 O+ were generated in a microwave gas discharge through an NH3 and H2 O vapour mixture and, after m/z selection, injected into He and N2 carrier gas. Using the conventional SIFT method, NH4 + reactions were then studied with M, the biogenic molecules acetone, 1-propanol, 2-butenal, trans-2-heptenal, heptanal, 2-heptanone, 2,3-heptanedione and 15 monoterpene isomers to obtain rate coefficients, k, and product ion branching ratios. Polarisabilities and dipole moments of the reactant molecules and the enthalpy changes in proton transfer reactions were calculated using density functional theory. The k values for the reactions of the biogenic molecules were invariably faster in N2 than in He but similar in both bath gases for the monoterpenes. Adducts NH4 + M were the dominant product ions in He and N2 for the biogenic molecules, whereas both MH+ and NH4 + M product ions were observed in the monoterpene reactions; the monoterpene ratio correlating (R2 =0.7) with the proton affinity, PA, of the monoterpene molecule as calculated. The data indicate that this adduct ion formation is the result of bimolecular rather than termolecular association. NH4 + can be a useful reagent ion for SIFT-MS analyses of molecules with PA(M) < PA(NH3 ) when the dominant single product ion is the adduct NH4 + M. For molecules with PA(M) > PA(NH3 ), such as monoterpenes, both MH+ and NH4 + M ions are likely products, which must be determined along with k by experiment.

Relative influence of helium and nitrogen carrier gases on analyte ion branching ratios in SIFT-MS

Nitrogen carrier gas is now being used more frequently for SIFT-MS analyses than helium for the reasons of cost and supply. Yet the extensive kinetics database required has largely been compiled using data obtained in helium carrier gas. This paper asks the question: can the helium-based kinetics library be used with confidence for analyses in nitrogen carrier gas? To investigate this, the rate coefficients and product ion distributions for the reactions of H3O+, NO+ and O2+● with three monoterpenes, β-pinene, camphene and (R)-(+)-limonene, and the specific reactions (a) H3O+ with 2-propanol, (b) O2+● with acetone, (c) NO+ with acetaldehyde and (d) NO+ with 2,3-butanedione have been explored in both helium and nitrogen carrier gases using a Profile 3 SIFT-MS instrument. These reactions were chosen because several primary reaction mechanisms are involved, including proton transfer (a), charge transfer (b), parallel hydride ion transfer and adduct ion formation (c) and parallel charge transfer and adduct ion formation (d). The detailed results show that for the diverse monoterpene reactions that have multiple product ions and for the pure bimolecular reactions (a) and (b), the reaction kinetics in both helium and nitrogen carrier gases are essentially identical. However, reactions (c) and (d) in which adduct ions are partially formed exhibit a slow carrier gas pressure dependence in helium, but a much greater carrier gas pressure dependence in nitrogen, and different product ion distributions. The conclusion is drawn that for pure bimolecular reactions, e.g. (a) and (b), the helium-obtained kinetics data can be used with confidence for trace gas analysis by SIFT-MS in nitrogen carrier gas, whereas kinetics data for ion-molecule reactions that involve adduct ion formation must be obtained by measurements under the specific pressure (and temperature) of the nitrogen carrier gas at which gas analyses are to be performed.

Phase transition of polybutene-1 ionomers: Influences of ion content and branch length

The phase transition behaviors from the tetragonal form II to the trigonal form I of polybutene-1 ionomers with various ion contents and branch lengths were studied by means of differential scanning calorimetry. In the ionomers studied, ionic functional groups were located at the end of the branches incorporated, so ion content was varied with the incorporation ratio and, branch length was tuned by the distinct co-monomers of 6-iodo-1-hexene and 18-iodo-1-octadecene. The results show that although the branches introduced retard the II-I phase transition in reference copolymers, after introduction of ions, the ionomers exhibit the largely accelerated kinetics of the solid II-I phase transition. Interestingly, it was found that the phase transition exhibits a non-monotonic dependence on the ion content and for the ionomers with 4-carbon branches, the optimal ion content to obtain the maximum transition degree is around 2.6 mol%. This is probably due to the cooperative effects of the formation of intercrystalline links by the ion aggregates in ionomers, 1) the enhanced transfer of internal stress for nucleation and 2) the restricted chain mobility for adjusting segmental packing. Furthermore, the II-I phase transition can be further accelerated by increasing the 4-carbon branch to the 16-carbon branch via copolymerizing 18-iodo-1-octadecene as the comonomers. These results provide the helpful guide to the molecular design of polybutene-1 ionomer materials.

Experimental and theoretical assessment of protonated Hoogsteen 9-methylguanine-1-methylcytosine base-pair dissociation: kinetics within a statistical reaction framework.

We investigated the collision-induced dissociation (CID) reactions of a protonated Hoogsteen 9-methylguanine-1-methylcytosine base pair (HG-[9MG·1MC + H]+), which aims to address the mystery of the literature reported "anomaly" in product ion distributions and compare the kinetics of a Hoogsteen base pair with its Watson-Crick isomer WC-[9MG·1MC + H]+ (reported recently by Sun et al.; Phys. Chem. Chem. Phys., 2020, 22, 24986). Product ion cross sections and branching ratios were measured as a function of center-of-mass collision energy using guided-ion beam tandem mass spectrometry, from which base-pair dissociation energies were determined. Product structures and energetics were assessed using various theories, of which the composite DLPNO-CCSD(T)/aug-cc-pVTZ//ωB97XD/6-311++G(d,p) was adopted as the best-performing method for constructing a reaction potential energy surface. The statistical Rice-Ramsperger-Kassel-Marcus theory was found to provide a useful framework for rationalizing the dominating abundance of [1MC + H]+ over [9MG + H]+ in the fragment ions of HG-[9MG·1MC + H]+. The kinetics analysis proved the necessity for incorporating into kinetics modeling not only the static properties of reaction minima and transition states but more importantly, the kinetics of individual base-pair conformers that have formed in collisional activation. The analysis also pinpointed the origin of the statistical kinetics of HG-[9MG·1MC + H]+vs. the non-statistical behavior of WC-[9MG·1MC + H]+ in terms of their distinctively different intra-base-pair hydrogen-bonds and consequently the absence of proton transfer between the N1 position of 9MG and the N3' of 1MC in the Hoogsteen base pair. Finally, the Hoogsteen base pair was examined in the presence of a water ligand, i.e., HG-[9MG·1MC + H]+·H2O. Besides the same type of base-pair dissociation as detected in dry HG-[9MG·1MC + H]+, secondary methanol elimination was observed via the SN2 reaction of water with nucleobase methyl groups.

Interpretation of flush-mounted probe current-voltage characteristics using four-parametric fits

The evaluation of probe measurements in the swept regime can be performed via a fit to the ion branch of the current-voltage (I–V) characteristic, providing the most relevant plasma parameters such as the ion saturation current, the electron temperature and the floating potential. In this paper, we present a parametric study based upon the existing flush-mounted probe setup briefly operated at the COMPASS tokamak, aiming to compare relevant I–V formulas widely used for such analysis. Selected four-parametric fit descriptions were applied to synthetic data obtained by simulation of the probe in a particle-in-cell model, SPICE, both in simplified 2D and more complex 3D geometries. Plasma parameters recovered by the fit were compared to the input from the model and the precision of this recovery was mapped to a wide range of parameters, especially with respect to the ratio of the probe size dpin to the Larmor radius rL. Results show that while the electron temperature and the floating potential can be obtained quite precisely regardless of the method, the ion saturation current can be identified incorrectly, mainly due to the fact that the sheath expansion description by optical approximation is not sufficient for almost grazing field line angles of incidence, especially when dpin ∼ rL. We show, however, that operation of flush-mounted probes can be fruitful especially in high-field devices. Additionally, we have explored the sensitivity on the available bias potential range, showing that for proper analysis of I–V characteristic using four-parametric fit, the lower bound of the fit range should be at least below the floating potential. If this condition cannot be satisfied, three-parametric fit in the range close to the floating potential can still produce results with acceptable precision.

PTR-MS studies of the reactions of H3O+ with a number of deuterated volatile organic compounds and the subsequent sequential reactions of the primary product ions with water under normal and humid drift tube conditions: Implications for use of deuterated compounds for breath analysis

Product ion distributions resulting from the primary reactions of H3O+ with nine D-labeled volatile organic compounds and the subsequent sequential reactions with H2O have been determined using a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF 8000 (IONICON Analytik GmbH)) at various reduced electric field (E/N) values ranging from 80 up to 150 Td and for two different absolute humidity levels of air sample < 0.1% and 5%. The specific D-labeled compounds used in this study are acetone-d6, toluene-d8, benzene-d6, ethanol-d (C2H5OD), ethanol-d2 (CH3CD2OH), ethanol-d6, 2-propanol-d8, 2-propanol-d3 (CD3CH(OH)CH3), and isoprene-d5 (CH2CHC(CD2)CD3). With the exception of the two 2-propanol compounds, non-dissociative proton transfer is the dominant primary reaction pathway. For 2-propanol-d8 and 2-propanol-d3 the major primary reaction channel involved is dissociative proton transfer. However, unlike their undeuterated counterparts, the primary product ions undergo subsequent deuterium/hydrogen isotope exchange reactions with the ever present water in the drift tube, the extent of which of course depends on the humidity within that tube. This exchange leads to the generation of various isotopologue product ions, the product ion branching percentages of which are also dependent on the humidity in the drift tube. This results in complex mass spectra and the distribution of product ions leads to issues of reduced sensitivity and accuracy. However, the effect of D/H exchange considerably varies between the compounds under study. In the case of acetone-d6 it is very weak (< 1%), because the exchange process is not facile when the deuterium is in the methyl functional group. In comparison, the H3O+/ benzene-d6 (C6D6) reaction and sequential reactions with water result in the production of the isotopologue ions C6Dn(H7-n)+ (where n = 0–6). Changing the value of E/N and/or the humidity in the drift tube considerably affects the amount of the isotope exchange reactions and hence the resulting sequential product ion distributions. An important conclusion of the findings from this work is that care must be taken in the choice of an exogenous deuterated compound for use in breath pharmacokinetic studies using proton transfer reaction mass spectrometry; otherwise the resulting D/H exchange processes impose interpretative problems.

Some experiments with the tunnel probe in a low temperature magnetized plasma

Experiments were performed using a Tunnel Probe (TP) inside the weakly-ionised plasma of the Linear Magnetized Plasma Device (LMPD). The TP is designed as a concave probe, which should annihilate the problem of sheath expansion in the ion branch of the I-V characteristic. As the ion saturation current is consequently well defined, the ion parallel current and plasma density can be more accurately calculated. Furthermore the ratio between the ion saturation currents on the two collectors (tunnel ring and the back-plate) can be used to derive the electron temperature. The TP has been repeatedly used with success on the former Castor and Tore-Supra tokamaks and will be used on the upgraded version of Tore-supra, namely the WEST tokamak, as well [1, 2]. It was however never used successfully in a low-temperature plasma.We studied the feasibility of the TP use in a low-temperature plasma for direct measurements of plasma temperature and density. The various probe characteristic dimensions, such as the distance between the two collectors, the aperture size and the probe radius were varied to see influence of the individual probe feature. We also varied the level of magnetization of the charged particle species, the background gas pressure (which influences the electron energy distribution function), the plasma density (important for the ratio between the λD and the ion Larmor radius). The sensitivity of the probe alignment to the magnetic field lines was also studied. We found, that the ion saturation current does not necessarily saturate and that the probe works according to expectations only in a limited amount of regimes.

A detailed study of the ion chemistry of alkenes focusing on heptenes aimed at their SIFT-MS quantification

Analyses of trace amounts of alkene vapours present in exhaled breath are becoming important in clinical research related to inflammatory bowel disease, IBD, currently affecting over 1 million patients in the USA and 2.5 million in Europe. Concentrations of alkenes have been previously found to be different in the breath of IBD patients in comparison with healthy controls and are suggested as potential biomarkers of IBD activity. Thus, a detailed selected ion flow tube, SIFT, study of the reactions of H3O+, NO+ and O2+ with a homologous series of alkenes (from 1-hexene to 1-decene) and with additional isomers of heptene (trans-2-heptene and a mixture of cis- and trans-3-heptene) has been carried out. The rate coefficients of all primary reactions and product ion branching ratios of the reactions of H3O+ and NO+ ions were obtained, which are necessary for accurate quantification of alkenes by selected ion flow tube mass spectrometry, SIFT-MS. The results of the present study facilitate analyses of these compounds in real breath samples with the ultimate aim of establishing their clinical use.

Comparisons and applications of four independent numerical approaches for linear gyrokinetic drift modes

To help reveal the complete picture of linear kinetic drift modes, four independent numerical approaches, based on the integral equation, Euler initial value simulation, Euler matrix eigenvalue solution, and Lagrangian particle simulation, respectively, are used to solve the linear gyrokinetic electrostatic drift mode equation in Z-pinch with slab simplification and in tokamak with a ballooning space coordinate. We identify that these approaches can yield the same solution with the difference smaller than 1%, and the discrepancies mainly come from the numerical convergence, which is the first detailed benchmark of four independent numerical approaches for gyrokinetic linear drift modes. Using these approaches, we find that the entropy mode and interchange mode are on the same branch in Z-pinch, and the entropy mode can have both electron and ion branches. And, at a strong gradient, more than one eigenstate of the ion temperature gradient mode (ITG) can be unstable and the most unstable one can be on non-ground eigenstates. The propagation of ITGs from ion to electron diamagnetic direction at strong gradient is also observed, which implies that the propagation direction is not a decisive criterion for the experimental diagnosis of turbulent mode at the edge plasmas.

Selective reagent ion-time of flight-mass spectrometry study of six common monoterpenes

One of the most common volatile organic compounds (VOCs) group is monoterpenes. Monoterpenes share the molecular formula C10H16, they are usually cyclic and have a pleasant smell. The most common monoterpenes are limonene (present in citrus fruits) and α-pinene (present in conifers’ resin). Different monoterpenes have different chemical, biological and ecological properties thus it is experimentally very important to be able to differentiate between them in real time. Real time instruments such as Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS), offer a real time solution for monoterpene measurement but at the cost of selectivity resulting in all monoterpenes being seen at the same m/z. In this work we used Selective Reagent Ion-Time of Flight-Mass Spectrometry (SRI/PTR-ToF-MS) in order to explore the differences in ion branching when different ionizations (H3O+, NO+ and O2+) and different drift tube reduced field energies (E/N) were used. We report a comprehensive ion library with many unique features, characteristic for individual monoterpenes.

Implementation and characterization of an RF ion funnel ion guide as a proton transfer reaction chamber

A radio frequency ion funnel reaction chamber is applied for use with a proton transfer reaction ion trap mass spectrometer (PIT-MS). The improvement in sensitivity over our dc-only drift tube ranged from 7.2x for isoprene to 65x for benzene. The ideal settings of the ion funnel are found to be a dc voltage of 60V, RF voltage of 240V and a pressure of 1.80mbar. An experimental and theoretical investigation of the ion funnel is presented. Simulations using SIMION and experimental measurements of the m/z dependent transmission of the ion funnel are performed, as well as simulations of the trajectories of ions and their survival probability. These are used to deduce a greater understanding of the operation of the ion funnel and the sensitivity improvements. The funnel is shown to favor transmission of higher m/z, and to increase sensitivity by a combined effect of focusing and increased effective reaction time. The product ions of an example set of compounds are measured systematically and the reagent ion branching profiles studied and compared to ion trap fragmentations. This represents an important undertaking in the characterization studies of ion funnel technology for use in PTR-MS.

Ion chemistry at elevated ion-molecule interaction energies in a selected ion flow-drift tube: reactions of H3O+, NO+ and O2+ with saturated aliphatic ketones.

The reactions of H3O+, NO+ and O2+ ions with a homologous series of six aliphatic ketones, viz. acetone through 2-octanone, have been investigated in a helium-buffered selected ion flow-drift tube, SIFDT, in order to reveal their dependencies on ion-molecule interaction energies, Er, and to gain insight into their mechanisms. The ultimate motivation is to allow analysis and absolute quantification of trace amounts of ketones and other volatile organic compounds in air using selected ion flow-drift tube mass spectrometry, SIFDT-MS. The reactions of H3O+ with the ketone molecules, M, proceed via exothermic proton transfer producing MH+ ions, the collisional rate coefficients, kc, for which can be calculated as a function of Er and are seen to reduce by about one third over the Er range from 0.05 eV up to 0.5 eV. The rate coefficients, k, and product ion distributions for the NO+ and O2+ reactions with M had to be obtained experimentally relative to the calculated kc for the H3O+ reactions. The product ions of the NO+/ketones reactions initially proceed via the formation of excited (NO+M)* adduct ions that partially fragment, and the k reduces with Er as much as four times for the acetone reactions but remains close to their respective kc for the higher-order ketones indicating long lifetimes of the (NO+M)* ions with respect to the stabilising collision times with He atoms. The k for the O2+/ketones dissociative charge transfer reactions are observed to be greater than their calculated kc implying that long distance electron transfer occurs.

Evaluation of ion current density distribution on an extraction electrode of a radio frequency ion thruster

The radial distributions of ion current density on an ion extracting electrode of a radio frequency (RF) ion thruster (RIT) with an inductive plasma source were obtained using probe diagnostics of the RF xenon plasma. Measurements were carried out using a plane wall probe simulator and the VGPS-12 Probe System of Plasma Sensors Co. At xenon flow rate q = 2 sccm plasma pressure was 2 · 10−3 Torr, incident RF generator power varied in the range Pg = 50−250 W with RF power absorbed by plasma up to Pp = 220 W. Ion current densities were determined using semi- and double-logarithmic probe characteristics by linear extrapolations of their ion branches to probe floating potentials. The same parameters were also measured in undisturbed plasma by a classic cylindrical probe. They exceeded plane probe data by more than two times, showing the effectiveness of plasma sheath reproduction of the RIT ion extracting electrode by the plane wall probe simulator. Slight non-uniformity of the resulting plasma distributions and simplified RIT model design showed that the studied device with flat antenna coil and ferrite core could be considered as a promising prospect for RITs of new generation.