Reaction of Aln clusters with oxygen and ammonia

Aluminum clusters were generated by a laser vaporization method. Ionization potential of Al₂ was found to be lower than that of Al. In the reaction with oxygen at high concentration, the mixed cluster Al₉O₇ survives predominantly as a stable cluster. Ammonia was found to be adsorbed weakly on the Al_n surface.     

Reaction dynamics of Na n + in collision with molecular oxygen

Reaction dynamics of sodium cluster ions, Na _n ⁺ (n = 2–9), in collision with molecular oxygen, O₂ was investigated by measuring the absolute dissociation cross sections and the branching fractions by using a tandem mass spectrometer equipped with several octapole ion guides. The mass spectrum of the product ions show that the dominant reaction channels are production of oxide ions, Na_kO_i (i =1, 2), and intact ions, Na _p ⁺ (p < n). With increase in the collision energy, the cross section for the production of the oxide ions decreased, while that for the production of the intact ions increased. The collision-energy dependences of the cross section for the oxide formation reveals that electron harpooning from the molecule to Na _n ⁺ preludes the oxideion formation. On the other hand, the collision-energy dependences of the cross sections for the intact ion formation is explained by a hard-sphere-collision model similar to the collisional dissociation of Na _n ⁺ by rare-gas impact.     

Evaluation of measurement uncertainty in the elemental analysis of sintered silicon carbide using laser ablation in liquid—inductively coupled plasma mass spectrometry with external calibration and isotope dilution

Accreditation and Quality Assurance - The goal of this study was to evaluate the uncertainty of elemental analytical methods that use laser ablation in liquid (LAL) as a pretreatment. After LAL...     

Photo-induced reactions of hemin (DMSO) n clusters (n = 0-3) produced with electrospray ionization

Photo-induced reaction of [Fe(III)-protoporphyrin]⁺ (hemin⁺) ions solvated with dimethylsulfoxide (DMSO) is investigated by using a tandem mass spectrometer with electrospray ionization. We measure the photodissociation yields of mass-selected hemin⁺(DMSO)_n clusters for n = 0-3 in the energy region of 15 800-28 200 cm^-1. The mass spectra of the fragment ions show the β-cleavage of carboxymethyl groups in addition to the evaporation of solvent molecules. Yield of the β-cleavage reaction is found to depend strongly on the excitation energy and the number of solvent molecules. We also examine the metastable decomposition of the clusters following primary mass selection and determine the incremental solvent binding energies and internal energies for the clusters using evaporative ensemble model. From these results, we investigate the reaction mechanism of β-cleavage of hemin⁺ ion.     

Precise determination of dissolved silica in seawater by ion-exclusion chromatography isotope dilution inductively coupled plasma mass spectrometry

Ion exclusion chromatograph (IEC) isotope dilution (ID) inductively coupled plasma mass spectrometry (ICP–MS) (IEC–ID–ICP–MS) was developed for measurement of dissolved silica in seawater, which was applied to production of certified reference materials (CRMs) of three concentration levels of nutrients (high, medium and low levels). IEC–ICP–MS has been employed to separate dissolved silica from seawater matrix. In the present study, in order to solve substantial problems due to spectral interference in ICP–MS and to improve the accuracy of IEC–ICP–MS beyond standard addition or conventional calibration methods, ID method was coupled with ICP-sector field mass spectrometry (operated under medium resolution,i.e., m/Δm = 4000). In addition, effects of various operating parameters in ICP–MS on a silicon background level were also investigated to obtain lower background equivalent concentration (BEC). As a result, 3 ng g⁻¹ of the BEC and 0.5 % of relative standard uncertainties were achieved in the analyses of dissolved silica in seawater samples at concentration levels from 4.0 mg kg ^-1 to 0.8 mg kg⁻¹ as silicon. The developed method was successfully validated by analyses of an artificial seawater containing a known amount of silicate and the seawater certified reference material MOOS-2 produced by the National Research Council Canada.     

Reactivity of positively charged cobalt cluster ions with CH4, N2, H2, C2H4, and C2H2

Reactivity of positively charged cobalt cluster ions (Co _n ⁺ ,n=2?22), produce by laser vaporization, with various gas samples (CH₄, N₂, H₂, C₂H₄, and C₂H₂) were systematically investigated by using a fast-flow reactor. The reactivity of Co _n ⁺ with the various gas samples is qualitatively consistent with the adsorption rate of the gas to cobalt metal surfaces. Co _n ⁺ highly reacts with C₂H₂ as characterized by the adsorption rate to metal surfaces, and it indicates no size dependence. In contrast, the reactions of Co _n ⁺ with the other gas samples indicate a similar cluster size dependence; atn=4, 5, and 10?15, Co _n ⁺ highly reacts. The difference can be explained by the amount of the activation energy for chemisorption reaction. Compared with neutral cobalt clusters, the size dependence is almost similar except for Co ₄ ⁺ and Co ₅ ⁺ . The reactivity enhancement of Co ₄ ⁺ and Co ₅ ⁺ indicates that the cobalt cluster ions are presumed to have an active site for chemisorption atn=4 and 5, induced by the influence of positive charge.     

Collision-induced reactions of size-selected molecular cluster anions

Collision-induced reactions of size-selected cluster anions, (CO₂) _n ^? and (N₂O)_nO^? with He and Kr atoms were studied at collision energies from 0.1 to 2.0 eV (center-of mass) by means of a tandem mass-spectrometer equipped with a pair of octapole ion guides. The dominant process was evaporation of the constituent molecules from the parent cluster ion. The absolute cross section for the evaporation was measured as functions of the size of the parent cluster ion and the collision energy. The reaction was explained by collisional excitation of the parent cluster ion followed by its unimolecular dissociation. The observed cross sections which correspond to those for the collisional excitation agree with those calculated in terms of charge-induced dipole and induced dipole-induced dipole interactions between the parent cluster ion and the target atom. The distributions of the product ions resulting from the unimolecular dissociation were reproduced by a simple calculation based on RRK theory. In the collision of (CO₂) _n ^? , the cross sections for (CO₂) ₁₀ ^? and (CO₂) ₁₄ ^? were significantly small and their abundances in the product ion distributions were particularly large. These findings indicate that (CO₂) ₁₀ ^? and (CO₂) ₁₄ ^? are stable species. On the other hand, stable species in (N₂O)_nO^? was found to be (N₂O)₅O^?.     

Collisional process involving atomic cluster ions

Collision of Ar cluster ions, Ar _n ⁺ (n=3–16), with He and Ne atoms was investigated by use of mass spectroscopic techniques. The cross sections for the production of Ar _n ⁺ (nn) were measured as functions of the size of the parent cluster ion and the collision energy (0.1–10 eV in the center-of-mass frame). These results were analyzed in the scheme of hard-sphere spectator collision with RRK theory. It was concluded that the reaction proceeds via collisional excitation of the parent cluster ion and following sequential loss of the constituent Ar atoms.This paper was originally submitted in connection with the 2nd. Int. Conference on Atomic and Nuclear Clusters held in Santorini from 28. June-2. July 1993 and is published here as a regular article after an independent refereeing procedure according to the standards of Z. Phys. D     

Structures and reactions of hydrated biomolecular cluster ions

Photo-induced reactions and metastable decompositions of cluster ions containing glycine, tryptophan, tryptophanylglicine and [Fe(III)-protoporphyrin]⁺ (hemin⁺) ions solvated with water molecules are studied with electrospray ionization (ESI). The ESI ion source is improved to produce hydrated biomolecular cluster ions. Metastable decompositions of the hydrated clusters following primary mass selection are measured to determine the incremental solvent binding energies for the clusters by using evaporative ensemble model. From these experimental findings, stability of the cluster ions is discussed in terms of delocalization of ionic charges. We also measure the photodissociation yields of mass-selected water clusters containing hemin⁺ ions at 355 and 532 nm. The mass spectra of photofragments show the β-cleavage of carboxymethyl groups in addition to the evaporation of solvent molecules.     

Improved accuracy of determination of dissolved silicate in seawater using absorption spectrometry

We studied to develop a certified reference material of seawater for nutrient analysis whose relative combined standard uncertainty for dissolved silicate was <0.5 %. In order to precisely measure the content of dissolved silicate in seawater, widely used absorption spectrometry with the so-called molybdenum blue was investigated as one of the highly sensitive determination methods. For the absorption spectrometry, a batch mode and a continuous flow analysis (CFA) mode were used and the characteristics of the calibration curves in the both modes were examined in detail. The calibration curve in the batch mode could be explained by a first-order regression line, whereas that in the CFA mode fitted to a second-order regression line. Therefore, for measuring the silicate content of seawater whose matrix depends on its origin, a standard addition method in a batch mode is preferable, though strict control of the compositions of the solutions for the standard addition calibration curve are greatly important for getting good linearity of the curve. In addition, in the case of the standard addition method, it is important to measure the blank value including the background; in the present study, the origins related to the blank were discussed and evaluated. The relative combined standard uncertainty of 0.48 % could be achieved for the measurement of content of 28 μmol/kg silicate in seawater, providing that the volume ratio between each of the molybdenum blue colorimetric reagents and the seawater was kept constant among all the solutions for the standard addition calibration curve. The procedure was validated using artificial seawater with a known concentration of silicate. Such highly improved precision and trueness which reaches the recent target of the community related to analysis of nutrients in seawater is reported for the first time. The developed procedure will provide a good way of validation for the analysts who need measurement with high precision and trueness on the content of silicate in seawater and other samples.