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1.
Metastable ion and collisionally-activated dissociation spectra of several cluster ions of the type [Csn+1In]+, formed by fast atom bombardment mass spectrometry (FABMS) of CsI, have been studied: It is found that particular cluster ions are more stable than others. Less stable ions undergo more unimolecular dissociation and have larger cross-sections for collisional dissociation than do the more stable ions, and this leads to unexpected anomalies in the FAB mass spectrum of CsI. The collision spectrum of [Cs35I34]+ (m/z 8966) has been acquired at an accelerating potential of 10 kV; the extent of both unimolecular and collisionally-activated dissociation of this ion is remarkably high and leads to collision/ transmission efficiencies of 85% for our tandem mass spectrometer. Clusters formed by FAB of an equimolar mixture of CsI and KI have also been studied by their collisionally-activated dissociation (CAD) and metastable ion (MI) spectra.  相似文献   

2.
The generation and unimolecular fragmentation of V n + and Nb n + clusters formed in sputtering vanadium and niobium surfaces by Xe+ ions has been studied. The method of measuring the kinetic energy of fragment ions (kinetic energy release distribution) has been used to determine the dissociation energy. Kinetic energy spectra have been measured in the field-free zone (corresponding to a time window of 10−5–10−4 sec after emission) of an ion microanalyzer with double focusing in reverse geometry. The results of spectra measurement were treated using the Rice-Ramsperge-Kassel theory of unimolecular reactions and the “evaporative ensemble”, which allowed us to calculate the dissociation energies of homonuclear V n 1 (n= 5–11) and Nb n 1 (n = 3–8) clusters.  相似文献   

3.
It is known that a niobium-carbon Met-Car cluster ion (Nb 8C 12 (+)) and its intermediates (Nb 4C 4 (+), Nb 6C 7 (+), etc.) are selectively formed by the aggregation of the Nb atoms in the presence of hydrocarbons. To elucidate the formation mechanism, we prepared Nb n C m (+) with every combination of n and m in the gas phase by the laser vaporization technique. The reactivity of Nb n C m (+) with H 2 was examined under the multiple collision condition, finding that Nb n C m (+) between Nb 2C 3 (+) and Nb 8C 12 (+) are not reactive with H 2. On the basis of the H 2 affinity of Nb n C m (+) experimentally obtained, we propose a dehydrogenation-controlled formation mechanism of niobium-carbon Met-Car cluster ions.  相似文献   

4.
Metastable decay of cluster ions has been discovered only recently. It was noted that one has to take this metastable decay into account when using mass spectrometry to probe neutral clusters, because ion abundance anomalies in mass spectra of rare gas and molecular clusters are caused by delayed metastable evaporation of monomers following ion production. Moreover, it was found that(i) the individual metastable reaction rates k depend strongly on cluster size and cluster ion production pathways and that(ii) there exists experimental evidence (k=k(t)) and a theoretical prediction that a given mass selected cluster ion generated by electron impact ionization of a nozzle expansion beam will comprise a range of metastable decay rates. In addition, it was discovered that metastable Ar cluster ions which lose two monomers in the μs time regime decay via sequential decay series Ar n + *→Ar n?1 + *→Ar n?2 + * with cluster sizes 7≤n≤10 andn=3 (similar results were obtained recently in case of N2 cluster ions). Conversely, the dominant metastable decay channel of Ar 4 + * into Ar 2 + was found to proceed predominantly via a single step fissioning process.  相似文献   

5.
Silver iodide clusters have been generated by inert gas condensation technique, ionized via electron impact, and mass analyzed in a reflectron equipped time-of-flight mass spectrometer. The mass spectra are dominated by cluster ions of the composition (AgnIn?1)+. Additional kinetic energy analysis is applied to detect metastable decay of the cluster ions for n up to 30. In contrast to alkali halides, where halogen and monomer desorption had been observed, the main decay channel of silver iodide cluster ions is the loss of a neutral trimer Ag3I3.  相似文献   

6.
A fast and selective method has been developed for the separation of the iodine fission products in the primary cooling water of nuclear reactors. The parameters of the selective retention were studied on silver, thallium(I) and mercury(II) iodide. Retention experiments were performed on adequately thick layers of “free” precipitates and on precipitates fixed in filter paper. The latter method substantially increases the retention capacity. The papers with fixed precipitate are easy to handle. The filter paper with silver iodide precipitate was found to be the most satisfactory for the selective retention of fission iodine from reactor water.  相似文献   

7.
O to N Alkyl migration in 1-aryl-5-alkoxytetrazoles was observed on healing the substrates in the presence of sodium iodide. Unlike in similar rearrangements, methyl transfer did not occur in the presence of methyl iodide alone. Solvent effects were also investigated.  相似文献   

8.
The intensity distribution of benzene+-Arn cluster ions formed by laser ionization of neutral clusters has been investigated: two main intensity anomalies (magic numbers atn=20 and 45) have been observed in the 15–60 size range. The evaporation dynamics of these species in the 2–50 microsecond time window following ionization has been studied using the electrostatic mirror of a reflectron time-of-flight mass spectrometer as a kinetic energy analyser capable to distinguish parent and daughter ions. The magic numbers are interpreted in terms of size dependent evaporation behaviors: beyondn=20, a sudden decrease of the evaporation energy is observed; in then=45–47 size range, the magic number is accounted for by the specific dynamics of then=46 and 47 clusters, in particular the possible loss of two argon atoms forn=47 within the experimental time window. These results and their implications on the cluster structure are discussed in the light of the evaporative ensemble model and compared to the evaporation characteristics of similar species, in particular the neat rare gas clusters.  相似文献   

9.
MALDI mass spectrometric characterization of sulfated glycans is often challenging due to their low ionization response in the positive ion mode. Here we demonstrate a new analytical approach, allowing the measurement of sulfated glycans by substituting the sulfate group with a deuteromethyl group. Sulfated glycan samples are initially permethylated before the methanolytic cleavage of their sulfate groups. Desulfated and permethylated glycans are then subjected to another permethylation step using deuteromethyl iodide to label the hydroxyl groups resulting from methanolysis. The number of attached sulfate groups is subsequently calculated from the mass-shift resulting from the chemical cleavage of these sulfate groups. The position of the sulfate substitution is then determined by collision-induced dissociation (CID) tandem mass spectrometry of permethylated and permethylated plus deuteromethylated samples. The described approach was initially optimized and validated using linear standard glycans, while its effectiveness has also been demonstrated here for the N-glycans derived from bovine thyroid-stimulating hormone (bTSH).  相似文献   

10.
Summary Selectivity is defined as the difference between the logarithms of distribution coefficients. The following examples of selective separations are presented: Compounds of silver for separation of iodine, cadmium sulphide for separation of technetium, titanium hexacyanoferrate for separation of caesium, polystyrene containing tetraphenylborate as functional group for separation of alkali ions.
Selektive Abtrennverfahren für Jod, Technetium, Cäsium und Alkaliionen
Zusammenfassung Die Selektivität wird definiert als Unterschied zwischen den Logarithmen der Verteilungskoeffizienten. Folgende Beispiele für selektive Abtrennungen werden beschrieben: Abtrennung von Jod mit Hilfe von Silberverbindungen, von Technetium mit Cadmiumsulfid, von Cäsium mit Titanhexacyanoferrat sowie von Alkaliionen mit tetraphenylborathaltigem Polystyrol.
Presented at the IUPAC International Congress on Analytical Chemistry, Kyoto 1972.  相似文献   

11.
Compound cluster ions of heavy post-transition atoms (In, Pb, As, Sb, Bi) are enriched by electron induced dissociation if they are analogous to the Zintl polyanions Pb 5 2? and Pb 9 4? with respect to the atom and valence electron number.  相似文献   

12.
The emission of secondary ions of about fifteen different elements, sputtered from Ti-base metal specimens, has been studied by SIMS. Both positive and negative ion yields have been measured at different exit energies up to ca 350 eV. It is found that when the logarithm of ionizability is plotted versus the inverse of the exit velocity, each element suggests a straight line behavior at energies above ca 20 eV. The gradient of the straight line is related to the respective 1st ionization potential (for positive ions) or electron affinity (negative ions). This behavior gives considerable support to the premises of modern theory of ionization in sputtering. Furthermore, the straight line plots for different elements are seen to converge as exit velocity increases; the intercepts at zero inverse velocity are found to be proportional to the respective element concentrations. This in principle offers a means of quantification in elemental analysis by SIMS, a method that does not require any external standards. The usefulness of the new method is demonstrated for ten elements sputtered from two specified titanium-base alloy standards from NIST.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday  相似文献   

13.
First results are presented from a new apparatus, consisting of a supersonic beam for generating neutral clusters, a variable energy electron gun for ionizing the clusters, and a tandem mass spectrometer set-up for studying surface induced reactions of mass and energy selected cluster ions. Rare gas cluster ions, fragment ions from SF6, benzene ions and benzene cluster ions have been investigated so far. Cluster ion dissociation, intracluster ion molecule reactions and surface reactions with adsorbed hydrocarbons have been shown to be important reaction channels for these ion-surface collision at energies ranging from a few eV to 500 eV. The surface induced fragmentation spectrum is demonstrated to be a useful tool for probing binding energy and structure of cluster ions.  相似文献   

14.
Botschwina P  Dutoi T  Mladenović M  Oswald R  Schmatz S  Stoll H 《Faraday discussions》2001,(118):433-53; discussion 487-503
Several proton-bound cluster ions have been studied by means of coupled cluster calculations with large basis sets. Among these are complexes of a krypton or xenon atom with the cations HCO+, HN2+ and HNCH+. Various spectroscopic properties have been calculated in all cases. Effects of vibrational anharmonicity are particularly pronounced for the intramolecular stretching vibrations of Kr...HN2+ and Xe...HN2+. The proton stretching vibration of (N2)H+(N2) is predicted around 800 cm-1, with a large transition dipole moment of 1.15 D. Both (N2)H+(N2) and (HCN)H+(NCH) have linear centrosymmetric equilibrium structures. Those of (OC)H+(CO) and (HCC-)H+(CCH-) are asymmetric with barrier heights to the centrosymmetric saddle points of 382 and 2323 cm-1, respectively. The dissociation energy of the anionic complex Cl-...HCCH is calculated to be Do = 3665 cm-1, 650 cm-1 larger than the corresponding value for Br-...HCCH. The complex between a fluoride ion and acetylene is more strongly bound and shows strongly anharmonic behaviour, similar to the bihalides FHF- or ClHCl-. Strong Fermi resonance interaction is predicted between nu 3 (approximately proton stretch) and 2 nu 4 (first overtone of intermolecular stretch).  相似文献   

15.
The 3-dimensional characterization of solids by means of secondary-ion mass spectrometry is investigated. Monitoring MCs+ molecular ions emitted from surfaces upon Cs+ bombardment, laterally-resolved ion images were recorded with acquisition times of typically a few seconds which exhibit a dynamic sensitivity range in excess of 102 and a lateral resolution of about 2–3 μm. A quantitative data evaluation via relative sensitivity factors (RSFs) transforms them into elemental distribution maps. From the applied RSFs, local (i.e. erosion-time dependent) sputtering yields can be derived; together with atomic densities (which might be interpolated from pure-element values) a local depth scale (relative to some reference level) is assigned to each pixel of the 3D data volume recorded during the analysis. In conjunction with the elemental concentration values, this provides the possibility of a complete reconstruction of the 3D sample volume removed by sputtering. This approach is exemplified by means of a laterally inhomogeneous semiconductor test specimen.  相似文献   

16.
《Chemical physics letters》1986,129(5):429-432
Absolute cross sections for reaction of aluminum atomic, dimer and trimer ions with oxygen, water and ethylene are reported. For all three reactions the dimer ion is by far the most reactive at low collision energies. The atomic ion is four to ten times less reactive and the trimer is non-reactive within our sensitivity. At higher collision energies the dimer reactivity drops and in some cases the atomic and trimer ion reactivities increase. Extensive fragmentation of the cluster ions is observed at collision energies above 3.0 eV.  相似文献   

17.
18.
Qualitative similarities and differences between metal cluster and nuclear fission are discussed in terms of the liquid drop model. Points covered include the dependence onz 2/n of the relative fission rate, the critical size, and the competition between fission and evaporation.  相似文献   

19.
廖晓垣 《化学学报》1986,44(7):652-658
本文对碘化钠-碘浓溶液体系中碘离子阳极氧化扩散电流的性质进行了研究.指出在这种体系中,阳极扩散电流下由碘离子向阳极的扩散速度所控制,而是由阳极电解产物碘由电极表面向溶液中的扩散所控制;其极限扩散电流密度与本文中定义的碘的未饱和度ΔmI2.max成正比,后者是一个与通常所指的碘的不饱和度在意义和数值上都不相同的物理量。  相似文献   

20.
The reaction of238U with12C was studied radiochemically with the purpose of elucidating fast fission characteristics. Fast fission component was extracted in far-asymmetric mass region and interpreted as the mass diffusion following the Fokker-Planck equation. Anomalous charge dispersion widths in the corresponding mass region and a sudden increase of the whole mass distribution width at the critical energy were also observed to support the above interpretation. The reaction time of fast fission was determined to be 5·10−21 s from the width and position of the mass distribution.  相似文献   

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