Cluster Ion Distributions Research Articles

Quantitative assessment of nano-plastic aerosol particles emitted during machining of carbon fiber reinforced plastic

Focusing on the relatively unexplored presence of micro- and nano-plastic aerosol particles, this study quantitatively assessed the emission of nano-plastic particles during the machining of carbon fiber reinforced plastic (CFRP) in the working environment. Measurements of aerosol particles smaller than 1 µm in size were performed by aerosol mass spectrometry. The findings revealed that concentrations of carbonous aerosol particles (organic aerosol and refractory black carbon (rBC)) were higher during working hours than during non-working hours. Positive matrix factorization identified CFRP particles as a significant source, contributing an average of approximately 30% of concentration of carbonous aerosol particles during working hours. This source apportionment was corroborated by the presence of bisphenol A and F fragments, principal components of the epoxy resins used in CFRP, and was corroborated by similarities to the carbon cluster ion distribution observed in rBC during CFRP pipe-cutting operations. Further, the particle size distribution suggested the existence of plastic aerosol particles smaller than 100 nm. This study established the method to quantitatively distinguish nano-plastic aerosol particles from other aerosol particles in high temporal resolution and these techniques are useful for accurately assessing exposure to nano-plastic aerosol particles in working environments.

Submersion of rubidium clusters in helium nanodroplets

Alkali atoms and small clusters are known to reside on the surface of a helium droplet rather than its inside as most other dopant species. A theoretical investigation suggested that alkali clusters (Li–Rb) exceeding a certain critical size can become submerged in the droplet, which was experimentally confirmed for sodium and potassium. Here, we report an analogous experimental study of rubidium cluster submersion by means of electron impact mass spectrometry. We recorded size distributions of Rb cluster ions at various electron energies between 8 and 160 eV. Our data suggest that Rb clusters attached to helium droplets undergo a gradual submersion transition similar to potassium, ultimately leading to the full submersion of clusters larger than sim 100~hbox {Rb} atoms. Our findings are consistent with previous theoretical and experimental studies.Graphic abstract

Reagent and analyte ion hydrates in secondary electrospray ionization mass spectrometry (SESI-MS), their equilibrium distributions and dehydration in an ion transfer capillary: Modelling and experiments.

Secondary electrospray ionization (SESI) in a water spray environment at atmospheric pressure involves the reactions of hydrated hydronium reagent ions, H3 O+ (H2 O)n , with trace analyte compounds in air samples. Understanding the formation and dehydration of reagent and analyte ions is the foundation for meaningful quantification of trace compounds by SESI-mass spectrometry (MS). A numerical model based on gas-phase ion thermochemistry is developed that describes equilibria in H3 O+ (H2 O)n reagent cluster ion distributions and ligand switching reactions with polar NH3 molecules leading to equilibrated hydrated ammonium ions NH4 + (H2 O)m . The model predictions are compared with experimental results obtained using a cylindrical SESI source coupled to an ion-trap mass spectrometer via a heated ion transfer capillary. Non-polar isoprene, C5 H8 , was used to further probe the nature of the reagent ions. Equilibrium distributions of H3 O+ (H2 O)n ions and their reactions with NH3 molecules have been characterized by the model in the near-atmospheric pressure SESI source. NH3 analyte molecules displace H2 O ligands from the H3 O+ (H2 O)n ions at the collisional rate forming NH4 + (H2 O)m ions, which travel through the heated ion transfer capillary losing H2 O molecules. The data for variable NH3 concentrations match the model predictions and the C5 H8 test substantiates the notion of dehydration in the heated capillary. Large cluster ions formed in the SESI region are dehydrated to H3 O+ (H2 O)1,2,3 and NH4 + (H2 O)1,2 while passing through the heated capillary, and considerable diffusion losses also occur. This phenomenon is also predicted for other polar analyte molecules, A, that can undergo similar switching reactions, thus forming AH+ and AH+ (H2 O)m analyte ions.

Mid carbon (C6+-C29+) in refractory black carbon aerosols is a potential tracer of open burning of rice straw: Insights from atmospheric observation and emission source studies

Abstract Biomass burning (BB) is one of the major sources of atmospheric aerosols. These aerosols cause global and regional issues such as adverse effects on human health, as well as contributing to climate change. Refractory black carbon (rBC) is a major chemical component emitted from BB. Recent studies indicate that the mass spectra distribution of carbon cluster ions (Cn+) in rBC reflects burning materials and combustion temperatures. Therefore, emissions apportionment is in principle possible with respect to rBC. However, emissions data for Cn+ are still not widely available. In this study, a combustion experiment using rice straw was conducted to identify the mass spectra of Cn+ measured using a soot particle aerosol mass spectrometer. Further, to confirm the results, atmospheric observations were conducted during the harvest season in a suburban area surrounded by rice fields because intentional open burning of rice straw (agricultural residues) is often conducted. Source apportionment of airborne ambient rBC generated from open burning of rice straw is carried out by a positive matrix factorization (PMF) method applied to hourly mean data for rBC and Cn+, as well as organic aerosols. During the atmospheric observation period, there was an intensive day of open burning of rice straw, confirmed by visual inspections around the observation site. Concentrations of PM2.5 reached up to 100 μg/m3 and the contribution of BB to rBC increased by up to 50% on that day. Tracers of BB (C2H4O2+ which is a fragment ion of levoglucosan and refractory K+ ions) were also enriched at that time. This study also found that the signal fraction of mid carbon (C6+-C29+) to total carbon (C1+-C35+) in rBC was 0.21 for dry rice straw burning. Correspondingly, the BB-related PMF factor in atmospheric observations (0.18) was close to the emission source data. Rice straw burning tends to occur at a low combustion temperature and generates amorphous (immature) soot, which was further confirmed by a larger value (0.41) for wet rice straw burning with low modification combustion efficiency. On the other hand, the mid carbon fraction of rBC from automobile exhausts (diesel and gasoline) was low (below 0.02) in laboratory studies and the automobile exhaust-related PMF factor was also relatively low (0.08) in atmospheric observations. These emissions are likely generated as graphite (mature) soot under a high combustion temperature. This study also quantifies and explores the atmospheric aging of BB aerosols. Decay rates of mid carbon were about 2 times slower than that of levoglucosan estimated from atmospheric observations. In sum, the mid carbon fraction can be used to differentiate sources of rBC emissions between open burning of rice straw at low combustion temperatures and other rBC sources at high combustion temperatures (such as internal combustion engines) on the one hand and estimate the decay rates of aerosols emitted from BB on the other hand.

An intense source for cold cluster ions of a specific composition.

The demand for nanoscale materials of ultra-high purity and narrow size distribution is addressed. Clusters of Au, C60, H2O, and serine are produced inside helium nanodroplets using a combination of ionization, mass filtering, collisions with atomic or molecular vapor, and electrostatic extraction, in a specific and novel sequence. The helium droplets are produced in an expansion of cold helium gas through a nozzle into vacuum. The droplets are ionized by electron bombardment and subjected to a mass filter. The ionic and mass-selected helium droplets are then guided through a vacuum chamber filled with atomic or molecular vapor where they collide and "pick up" the vapor. The dopants then agglomerate inside the helium droplets around charge centers to singly charged clusters. Evaporation of the helium droplets is induced by collisions in a helium-filled radio frequency (RF)-hexapole, which liberates the cluster ions from the host droplets. The clusters are analyzed with a time-of-flight mass spectrometer. It is demonstrated that using this sequence, the size distribution of the dopant cluster ions is distinctly narrower compared to ionization after pickup. Likewise, the ion cluster beam is more intense. The mass spectra show, as well, that ion clusters of the dopants can be produced with only few helium atoms attached, which will be important for messenger spectroscopy. All these findings are important for the scientific research of clusters and nanoscale materials in general.

Strong southward and northward currents observed in the inner plasma sheet

Abstract. It is generally believed that field-aligned currents (FACs) and the ring current (RC) are two dominant parts of the inner magnetosphere. However, using the Cluster spacecraft crossing the pre-midnight inner plasma sheet in the latitudinal region between 10 and 30∘ N, it is found that, during intense geomagnetic storms, in addition to FACs and the RC, strong southward and northward currents also exist which should not be FACs because the magnetic field in these regions is mainly along the x–y plane. Detailed investigation shows that both magnetic-field lines (MFLs) and currents in these regions are highly dynamic. When the curvature of MFLs changes direction in the x–y plane, the current also alternatively switches between being southward and northward. To investigate the generation mechanism of the southward and northward current, we employed the analysis of energetic particle flux up to 1 MeV. For energetic particles below 40 keV, observations from Cluster CIS/CODIF (Cluster Ion Spectrometry COmposition and DIstribution Function analyzer) are used. However, for higher-energy particles, the flux is obtained by extrapolations of low-energy particle data through Kappa distribution. The result indicates that the most reasonable cause of these southward and northward currents is the curvature drift of energetic particles.

The Nocturnal Positive Ionospheric Anomaly of Electron Density as a Short-Term Earthquake Precursor and the Possible Physical Mechanism of Its Formation

This paper summarizes the years of studies devoted to the self-similarity of anomalies originating in the ionosphere above the regions of the preparation of strong earthquakes. Using statistical processing of data on electron density variations obtained by methods of vertical sounding and measurements of the total electronic content, we have formed a pattern of similar variations observed at midlatitudes before strong earthquakes; we call it a precursor mask for earthquakes. It was found that the positive anomaly in the ionosphere formed at nighttime after sunset and ended at sunrise. In the case of strong earthquakes, the anomaly can last 12 h and emerge within a few days at the same local time. We propose a physical mechanism of anomaly formation in the ionosphere bound with the diurnal dynamics of the atmospheric boundary layer, which regulates the height distribution of cluster ions.

Positively and Negatively Charged Cesium and (C60) m Cs n Cluster Ions.

We report on the formation and ionization of cesium and C60Cs clusters in superfluid helium nanodroplets. Size distributions of positively and negatively charged (C60)mCsn± ions have been measured for m ≤ 7, n ≤ 12. Reproducible intensity anomalies are observed in high-resolution mass spectra. For both charge states, (C60)mCs3± and (C60)mCs5± are particularly abundant, with little dependence on the value of m. Distributions of bare cesium cluster ions also indicate enhanced stability of Cs3± and Cs5±, in agreement with theoretical predictions. These findings contrast with earlier reports on highly Cs-doped cationic fullerene aggregates which showed enhanced stability of C60Cs6 building blocks attributed to charge transfer. The dependence of the (C60)mCs3– anion yield on electron energy shows a resonance that, surprisingly, oscillates in strength as m increases from 1 to 6.

Water network-mediated, electron-induced proton transfer in [C5H5N ⋅ (H2O)n](-) clusters.

The role of proton-assisted charge accommodation in electron capture by a heterocyclic electron scavenger is investigated through theoretical analysis of the vibrational spectra of cold, gas phase [Py ⋅ (H2O)n=3-5](-) clusters. These radical anions are formed when an excess electron is attached to water clusters containing a single pyridine (Py) molecule in a supersonic jet ion source. Under these conditions, the cluster ion distribution starts promptly at n = 3, and the photoelectron spectra, combined with vibrational predissociation spectra of the Ar-tagged anions, establish that for n > 3, these species are best described as hydrated hydroxide ions with the neutral pyridinium radical, PyH((0)), occupying one of the primary solvation sites of the OH(-). The n = 3 cluster appears to be a special case where charge localization on Py and hydroxide is nearly isoenergetic, and the nature of this species is explored with ab initio molecular dynamics calculations of the trajectories that start from metastable arrangements of the anion based on a diffuse, essentially dipole-bound electron. These calculations indicate that the reaction proceeds via a relatively slow rearrangement of the water network to create a favorable hydration configuration around the water molecule that eventually donates a proton to the Py nitrogen atom to yield the product hydroxide ion. The correlation between the degree of excess charge localization and the evolving shape of the water network revealed by this approach thus provides a microscopic picture of the "solvent coordinate" at the heart of a prototypical proton-coupled electron transfer reaction.

Characterization of a Direct Sample Analysis (DSA) Ambient Ionization Source.

Water cluster ion intensity and distribution is affected by source conditions in direct sample analysis (DSA) ionization. Parameters investigated in this paper include source nozzle diameter, gas flow rate, and source positions relative to the mass spectrometer inlet. Schlieren photography was used to image the gas flow profile exiting the nozzle. Smaller nozzle diameters and higher flow rates produced clusters of the type [H + (H(2)O)(n)](+) with greater n and higher intensity than larger nozzles and lower gas flow rates. At high gas flow rates, the gas flow profile widened compared with the original nozzle diameter. At lower flow rates, the amount of expansion was reduced, which suggests that lowering the flow rate may allow for improvements in sampling spatial resolution.

Effective methods for the measurement of CsI cluster ions using MALDI-MS with suitable solvent combinations and additives.

A method to measure CsI cluster ions ((CsI)(n)Cs(+), (CsI)(n)I(-)) from CsI samples in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was developed with a 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene] malononitrile (DCTB) matrix and additives. Solvent combinations in which the CsI and DCTB solutions were miscible were effective in detecting CsI cluster ions at a mass range of over m/z 2000 and are associated with a characteristic spread of DCTB within the CsI/DCTB mixture. The addition of saccharides or sugar alcohols to the CsI/DCTB mixture improved the DCTB distribution and widened the mass distribution of CsI cluster ions up to m/z 10,000 in the linear mode.

Velocity distribution of mass-selected nano-size cluster ions

The paper reports on an experimental investigation of the ion velocity distribution function (IVDF) for mass-selected copper cluster ions with a diameter in the range 5–10 nm. The cluster ion beam is produced by a dc magnetron-based gas aggregation source. The measurements are carried out by means of a quadrupole mass filter combined with a basic retarding field analyser. The most probable cluster velocities are in the range 80–180 m s−1; decreasing with cluster size and increasing with buffer gas (Ar) flow. Experimental results are compared with the theoretical model of Smirnov et al. Noted discrepancies are explained by the interaction of clusters with buffer gas atoms outside the aggregation chamber during the passage from the orifice towards the detector. This interaction is not included in the theoretical model. Both positively and negatively charged clusters are investigated. The density ratio of positively to negatively charged clusters in the beam is evaluated from the measured IVDFs and compared with the theoretical model.

The mathematical principles and design of the NAIS – a spectrometer for the measurement of cluster ion and nanometer aerosol size distributions

Abstract. The paper describes the Neutral cluster and Air Ion Spectrometer (NAIS) – a multichannel aerosol instrument capable of measuring the distribution of ions (charged particles and cluster ions) of both polarities in the electric mobility range from 3.2 to 0.0013 cm2 V−1 s−1 and the distribution of aerosol particles in the size range from 2.0 to 40 nm. We introduce the principles of design, data processing and spectrum deconvolution of the instrument.

Electronic sputtering of LiF by Krypton (10 MeV/u): size dependent energy distributions of Li+(LiF)n clusters

A combination of imaging techniques (XY) and time-of-flight (TOF) spectroscopy was used to measure the complete velocity vector of sputtered positive secondary ions in collisions of Kr33+ (10.1 MeV/u) with well-prepared LiF single crystals in the electronic stopping regime. The energy distributions N(E) of the cluster ions (LiF)nLi+ (n ≥ 0) depend on the size of the ejecta: the maximum is slightly shifted towards lower energy with increasing cluster size n. The measured energy distributions of emitted cluster ions can be fitted by a Maxwell-Boltzmann function N(E) = AEexp(−βE). This could be an indication that the processes generating the sputtering are compatible with a thermal origin.

Difference in formation of carbon cluster cations by laser ablation of graphene and graphene oxide

The distributions of positive carbon cluster ions produced by laser ablation of graphene (G) and graphene oxide (GO) are found to be quite different. Under a typical experimental condition, narrow distributions of even-numbered clusters from C60+ to C162+ were observed for G, and broad distributions including even-numbered clusters from C100+ to C400+ and odd-numbered clusters from C189+ to C395+ were observed for GO. The threshold of laser energy for G is lower than that of GO. Further results of collision-activated dissociation mass spectrometry indicate that the cluster ions generated from G are structurally similar but are different with those generated from GO or nanodiamonds. It is proposed that the experimentally observed difference can be attributed to the different mechanisms behind the process. A top-down mechanism including both direct transformation of G to fullerene and fragmentation of large-sized fullerenes is suggested for the generation of carbon cluster cations in the process of laser ablation of G. For GO, the experimental results are close to those of nanodiamonds and other materials reported previously and can be explained by the generally accepted bottom-up mechanism.

Cluster ion emission from LiF induced by MeV Nq+ projectiles and 252Cf fission fragments

Ion cluster desorption yields from LiF were measured at PUC-Rio with ≈0.1 MeV/u Nq+ (q = 2,4,5,6) ion beams by means of a time-of-fight (TOF) mass spectrometer. A 252Cf source mounted in the irradiation chamber allows immediate comparison of cluster emissions induced by ≈65 MeV fission fragments (FF). Emission of (LiF)nLi+ clusters are observed for both the N beams and the 252Cf fission fragments. The observed cluster size n varies from 1 to 6 for Nq+ projectiles and from 1 to ≈40 for the 252Cf-FF. The size dependence of the Y(n) distributions suggests two cluster formation regimes: (i) recombination process in the outgoing gas phase after impact and (ii) emission of pre-formed clusters from the periphery of the impact site. The corresponding distribution of ejected negative cluster ions (LiF)nF− closely resembles that of the positive secondary (LiF)nLi+ ions. The desorption yields of positive ions scale as Y(n) ∼ q5. A calculation with the CASP code shows that this corresponds to a cubic scaling ∼Se3 with the electronic stopping power Se, as predicted by collective shock wave models for sputtering and models involving multiple excitons (Frenkel pair sputtering). We discuss possible interpretations of the functional dependence of the evolution of the cluster emission yield Y(n) with cluster size n, fitted by a number of statistical distributions.

Nanoalloy Formation of Ta-containing Trimetallic Small Clusters

Trimetallic cluster ions containing Ta and other metal elements were prepared in the gas phase by a triple laser-ablation technique in a controlled manner. We have measured the abundances and their thermal stabilities, using time-of-flight mass spectrometry. Taking advantage of specific abundance distribution of the trimetallic cluster ions (magic stoichiometry), relative to the distinguished stabilities, the coalescence or the segregation of Ta and the other elements in the subnanometer sized clusters was discussed. We found that Nb, W, and Mo, which are categorized as elements with a high heat of vaporization, readily coalesce with Ta, while V, Al, Co, and Pt, which are categorized as elements with a low heat of vaporization, tend to be segregated from Ta. Our experiments, along with the calculation by another research group, suggest that the binding energies of atoms are related to the coalescence or segregation of clusters in the gas phase.

Positive and negative cluster ions from liquid ethanol by fast ion bombardment

Secondary ion mass spectra have been measured for the first time for a liquid ethanol target bombarded by 2.0 MeV He(+) ions. Positive and negative ion spectra exhibit evidently a series of cluster ions of the forms [(EtOH)(n)H](+) and [(EtOH)(n)-H](-), respectively, in addition to light fragment ions from intact parent molecules. It was found that these cluster ions are produced only from liquid phase ethanol. Both positive and negative secondary ion spectra show similar cluster size distributions with almost the same decay slope. We also present for the first time the cluster ion distribution emitted from the liquid at different liquid temperatures.

High Irradiance Laser Ionization Mass Spectrometry for Direct Speciation of Iron Oxides

A novel method has been developed that allows the direct speciation analysis of iron oxides based on a modified laser ionization orthogonal time-of-flight mass spectrometer. Time resolved mass spectra were acquired for the investigation of elemental ions and oxide ions generated by a laser ionization source. Speciation methodologies, including the identification of characteristic ions and the use of ion abundance ratios were evaluated for the differentiation of the oxides. The influence of operating parameters on the distribution of cluster ions was investigated, and their mechanism of formation discussed.

A Comparative Study of Secondary Ion Emission from Water Ice under Ion Bombardment by Au+, Au3+, and C60+

Secondary ion emission from water ice has been studied using Au+, Au3+, and C60+ primary ions. In contrast to the gas phase in which the spectra are dominated by the (H2O)nH+ series of ions, the spectra from ice using all three primary ions are principally composed of two series of cluster ions (H2O)nH+ and (H2O)n+. Dependent on the conditions, the unprotonated series can dominate the spectra. Since in the gas phase (H2O)n+ is unstable with respect to the formation of the protonated ion series, the presence of the solid must provide a means to stabilize their formation. The cluster ion yields under Au+ bombardment are very low and can be understood in terms of sputtering on the borderline between linear cascade and thermal spike behavior. There is a 104 increase in yield across the whole spectrum compared to Au+ when Au3+ and C60+ species are used as primary ions. The character of the spectra differed between these two primary ions, but insights into the mechanism of secondary ion emission for both is discussed within an energy deposition framework provided by the fluid flow-based mesoscale energy deposition footprint (MEDF) model that predicts a cone-shaped zone of activation and emission. C60+ differs from Au3+ in that it delivers its energy closer to the surface, and it is argued this has consequences for the cluster ion distribution and yield. Increasing the ion dose by sputtering suppresses the yield of (H2O)n+ and increases the yield of the protonated ions in the small cluster region, whereas the yield in the large cluster regime is suppressed significantly. The three primary ions show rather different behavior, and this is discussed in the light of the sputtering models. Finally, negative ion spectra including cluster ions have been observed for the first time. C60+ delivers the highest yields, but these are less than 10 times the positive ion yields, probably because the O and OH fragment ions on which the clusters are based are easily neutralized by protons.