Cluster Ions (cluster + ion)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Cluster ion beam profiling of organics by secondary ion mass spectrometry , does sodium affect the molecular ion intensity at interfaces?

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2008
Felicia M. Green
The use of cluster ion beam sputtering for depth profiling organic materials is of growing technological importance and is a very active area of research. At the 44th IUVSTA Workshop on "Sputtering and Ion Emission by Cluster Ion Beams", recent results were presented of a cluster ion beam depth profile of a thin organic molecular layer on a silicon wafer substrate. Those data showed that the intensity of molecular secondary ions is observed to increase at the interface and this was explained in terms of the higher stopping power in the substrate and a consequently higher sputtering yield and even higher secondary ion molecular sputtering yield. An alternative hypothesis was postulated in the workshop discussion which may be paraphrased as: "under primary ion bombardment of an organic layer, mobile ions such as sodium may migrate to the interface with the inorganic substrate and this enhancement of the sodium concentration increases the ionisation probability, so increasing the molecular ion yield observed at the interface". It is important to understand if measurement artefacts occur at interfaces for quantification as these are of great technological relevance , for example, the concentration of drug in a drug delivery system. Here, we evaluate the above hypothesis using a sample that exhibits regions of high and low sodium concentration at both the organic surface and the interface with the silicon wafer substrate. There is no evidence to support the hypothesis that the probability of molecular secondary ion ionisation is related to the sodium concentration at these levels. © Crown copyright 2008. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd. [source]


ChemInform Abstract: Synthesis and Investigation of Plutonium Oxide Cluster Ions: PuxOy+ (x , 18).

CHEMINFORM, Issue 34 2001
John K. Gibson
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2003
Boris L. Milman
Cluster ions such as [Cat+X+nM]+ (n,=,0,4); [Cat-H+nM]+ (n,=,1,3); and [2(Cat-H)+X+nM]+ (n,=,0,2), where Cat, X, and M are the dication, anion, and neutral salt (CatX2), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H]+, one-electron reduction of the dication to form Cat+., demethylation of the paraquat cation to form [Cat-CH3]+, and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H]+ and its clusters) and odd-electron (mostly Cat+.) ions in ESI mass spectra of these pesticides. The [Cat+n,·,Solv]2+ doubly charged cluster ions, where n,,,2 and Solv is the solvent molecule (methanol and/or water), are only observed as very weak peaks in precursor ion CID spectra of the Cat2+ salt cation at low collision energy. The presence of an anion and a solvent molecule in a cluster is assumed to be related to existence of tight and loose ion pairs, respectively, in multiply charged droplets/ions formed by ESI. The results emphasize again the role of solution chemistry concepts such as acidity/basicity, redox power, and ion-pair formation, for ESI. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Low-energy irradiation effects of gas cluster ion beams

ELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 2 2008
Shingo Houzumi
Abstract A cluster-ion irradiation system with cluster-size selection has been developed to study the effects of the cluster size for surface processes using cluster ions. A permanent magnet with a magnetic field of 1.2 T is installed for size separation of large cluster ions. Trace formations at HOPG surface by the irradiation with size-selected Ar-cluster ions under an acceleration energy of 30 keV were investigated by scanning tunneling microscopy. Generation behavior of the craterlike traces is strongly affected by the number of constituent atoms (cluster size) of the irradiating cluster ion. When the incident cluster ion is composed of 100 to 3000 atoms, craterlike traces are observed on the irradiated surfaces. In contrast, such traces are not observed at all with the irradiation of the cluster ions composed of over 5000 atoms. Such behavior is discussed on the basis of the kinetic energy per constituent atom of the cluster ion. To study GCIB irradiation effects on macromolecules, GCIB was irradiated on DNA molecules absorbed on graphite surface. Using GCIB irradiation, many more DNA molecules were sputtered away compared with the monomer-ion irradiation. © 2008 Wiley Periodicals, Inc. Electron Comm Jpn, 91(2): 40,45, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10031 [source]


Formation and reactions of cluster ions from aromatic carboxylic acids together with amino acids

ISRAEL JOURNAL OF CHEMISTRY, Issue 2 2001
Anja Meffert
The cluster formation of several aromatic carboxylic acids, ferulic acid, vanillic acid, sinapinic acid, and 3,4-dihydroxybenzoic acid was investigated by means of laser desorption into a supersonic beam followed by multiphoton ionization-time-of-flight mass spectrometry. The formation of not only homogeneous clusters, but also of heterogeneous clusters with some small amino acids was studied. The different neutral clusters formed in the supersonic expansion were ionized by a multiphoton process employing either nano- or femtosecond laser pulses. Strong differences in the detection of cluster ions due to the laser pulse length employed for multiphoton ionization were observed. Only femtosecond activation led to mass spectra with intense signals of the cluster ions. In addition, in the case of femtosecond ionization, protonated amino acids were detected in the mass spectra. As direct ionization of the free amino acids is not possible under the chosen ionization conditions because they lack an adequate chromophore, these protonated amino acids are assumed to be formed via an intracluster proton transfer in the heterogeneous dimer and subsequent decay of the ionized cluster (dissociative proton transfer). Such well-known processes for heterogeneous clusters consisting of a substituted aromatic molecule and small polar solvent molecules may be involved in the matrixassisted laser desorption ionization (MALDI) process. [source]


UV laser-induced desorption mechanism analyzed through two-layer alkali halide samples

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2008
F. A. Fernández-Lima
Abstract Time of flight-mass spectrometry (TOF-MS) is used to analyze positive and negative desorbed ions generated by UV laser ablation of several alkali (X) halide (Y) salts. Most of the observed desorbed cluster ions have the structure (XY)nX+ or (XY)nY,. Their desorption yields decrease as exp(,kn), where k , 2 for both series, suggesting that the neutral component (XY)n plays the dominant role in the desorption process. Mass spectrum measurements were performed for compound samples in which two salts (out of CsI, RbI, KBr, KCl and KI) are homogeneously mixed or disposed in two superposed layers. The detection of small new ion species and large cluster ions of the original salts supports the scenario that the uppermost layers are completely atomized while deep layers are emitted colder and fragmented: It is proposed that ns-pulsed laser induced desorption of ionic salts occurs via two sequential mechanisms: (1) ejection of cations and anions in the hot plume, followed by recombination into new cluster ions and (2) ejection of relatively cold preformed species originated from deep layers or from periphery of the irradiated region. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Mass-selective vibrational spectroscopy of vanadium oxide cluster ions

MASS SPECTROMETRY REVIEWS, Issue 4 2007
Knut R. Asmis
Abstract A corner stone in the study of the size-dependent properties of cluster ions in the gas phase is their structural characterization. Over the last 10 years, significant progress has been in this research field because of significant advances in the gas phase vibrational spectroscopy of mass-selected ions. Using a combination of modern experimental and quantum chemical approaches, it is now in most cases possible to uniquely identify the geometric structure of cluster ions, based on the comparison of the experimental and simulated infrared spectra. In this article, we highlight the progress made in this research area by reviewing recent infrared photodissociation (IR-PD) experiments on small and medium sized (up to 30 atoms) vanadium oxide ions. © 2007 Wiley Periodicals, Inc., Mass Spec Rev. [source]


Monitoring chloramines and bromamines in a humid environment using selected ion flow tube mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2010
Wan-Ping Hu
The selectivity and sensitivity of selected ion flow tube mass spectrometry (SIFT-MS) for individual breath analysis of haloamines has been improved by heating the flow tube in a commercial instrument to around 106°C. Data is presented showing the marked reduction in the number density of water clusters of product ions of common breath metabolites that are isobaric with the product ions from monochloramine and monobromamine that are used to monitor the haloamine concentrations. These results have direct relevance to the real-time monitoring of chloramines in drinking water, swimming pools and food processing plants. However, once the isobaric overlaps from water cluster ions are reduced at the higher temperatures, there is no conclusive evidence showing the presence of haloamines on single breath exhalations in the mid parts per trillion range from examination of the breaths of volunteers. Copyright © 2010 John Wiley & Sons, Ltd. [source]


Role of the support material on laser desorption/ionization mass spectra

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2008
A. Gruszecka
We report the results of experimental studies on the effects of sample supports in laser desorption/ionization mass spectrometry (LDI-MS). LDI time-of-flight (TOF) mass spectra obtained for C60 and insulin samples deposited onto standard stainless steel substrate and/or onto some non-metallic materials (glass, scotch tape, floppy disc foil, Teflon foil, photocopy film), all recorded under identical, typical experimental conditions, have been compared with regard to their intensity and quality. The LDI investigations show that compared with stainless steel, glass and floppy disc foil sample supports boost (2,3.5 times) ion yields for C and C ions, respectively. The stainless steel and scotch tape sample supports are the best for the mass resolution of positive ions and the formation of (C60) (n,,,4) cluster ions, respectively. In the case of detection of insulin by matrix-assisted laser desorption/ionization (MALDI) we did not observe significant differences in sensitivity for the support materials tested. A mechanism of ion formation in the desorption plume is suggested. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Desorption sonic spray ionization for (high) voltage-free ambient mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2006
Renato Haddad
Sonic spray ionization is shown to create a supersonic cloud of charged droplets able to promote efficient desorption and ionization of drugs directly from the surfaces of commercial drug tablets at ambient conditions. Compared with desorption electrospray ionization (DESI), desorption sonic spray ionization (DeSSI) is advantageous since it uses neither heating nor high voltages at the spray capillary. DeSSI therefore provides a more friendly environment in which to perform ambient mass spectrometry (MS). DeSSI-MS is herein evaluated for the analysis of drug tablets, and found to be, in general, as sensitive as DESI-MS. The (high) voltage-free DeSSI method provides, however, cleaner mass spectra with less abundant solvent cluster ions and with enough abundant analyte signal for tandem mass spectrometry (MS/MS). These features may therefore facilitate the DeSSI-MS detection of low molar mass components or impurities, or both. The higher-velocity supersonic DeSSI spray also facilitates matrix penetration thus providing more homogenous sampling and longer lasting ion signals. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Reactions of platinum cluster ions with benzene

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2006
Hongtao Liu
In this work, the cation and anion products of the reactions between platinum clusters produced by laser ablation and the benzene molecules seeded in argon have been studied using a high-resolution reflectron time-of-flight mass spectrometer (RTOFMS). The dominant cation products are [C6nH6n,,,k]+ and [Ptm(C6H6)n]+ complexes, while the dominant anion products are dehydrogenated species, [C6H5PtH],, [PtC12Hk], and [PtmC6H4,·,·,·,(C6H6)n],, etc. Some important intermediate structures ([PtC6H6]+, [Pt(C6H6)2]+, [Pt2(C6H6)3]+, [C6H5PtH],, [Pt2C6H4],, [Pt3C6H4], and [Pt4C6H4],) have been analyzed using density functional theory (DFT) calculations. Different reaction mechanisms are proposed for platinum cluster cations and anions with benzene, respectively. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2003
Boris L. Milman
Cluster ions such as [Cat+X+nM]+ (n,=,0,4); [Cat-H+nM]+ (n,=,1,3); and [2(Cat-H)+X+nM]+ (n,=,0,2), where Cat, X, and M are the dication, anion, and neutral salt (CatX2), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H]+, one-electron reduction of the dication to form Cat+., demethylation of the paraquat cation to form [Cat-CH3]+, and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H]+ and its clusters) and odd-electron (mostly Cat+.) ions in ESI mass spectra of these pesticides. The [Cat+n,·,Solv]2+ doubly charged cluster ions, where n,,,2 and Solv is the solvent molecule (methanol and/or water), are only observed as very weak peaks in precursor ion CID spectra of the Cat2+ salt cation at low collision energy. The presence of an anion and a solvent molecule in a cluster is assumed to be related to existence of tight and loose ion pairs, respectively, in multiply charged droplets/ions formed by ESI. The results emphasize again the role of solution chemistry concepts such as acidity/basicity, redox power, and ion-pair formation, for ESI. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Forensic identification of explosive oxidizers by electrospray ionization mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2002
Xiaoming Zhao
The mass spectrometry of a group of inorganic oxidizers was studied using the electrospray ionization technique. It was found that a series of cluster ions were predominant in both positive- and negative-ion mode, allowing for the characterization of the investigated oxidizers. The identity of the recorded cluster ions was further confirmed by using some isotopically labeled compounds and tandem mass spectrometry with collision-induced dissociation. The use of electrospray ionization mass spectrometry for positive identification of major oxidizer components in explosive formulations was demonstrated by three samples of forensic interest. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Time-of-flight studies of secondary ions produced by 400,eV He+ ion impact on Ar, Kr, and Xe thin films at 8 K

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2002
Kenzo Hiraoka
Secondary ions produced by 400,eV He+ ion impact on Ar, Kr, and Xe thin films deposited on a silicon substrate at 8,K were measured as a function of film thickness using a time-of-flight secondary-ion mass spectrometer. For Ar, the cluster ions Arn+ up to n,=,4 as well as the monomer ion (n,=,1) were observed and they showed characteristic film-thickness dependence with increase of the film thickness up to ,200 monolayers. This is due to the momentum transfer in the elastic collision between the incident He+ ion and the matrix Ar atoms and also to the relaxation of electronic excitations (e.g., holes and excitons) to phonons resulting in the film erosion. In contrast, neither dimer nor cluster ions were detected for solid Kr and Xe films. This is due to the less efficient momentum transfer in the elastic collision between He+ and Rg's (Rg,=,Kr and Xe) and also to the efficient electronic energy migration in solid Kr and Xe. The ions originating from the silicon substrate such as Si+, SiCH3+, SiOH+, and C+ were found to be sensitized by the deposition of Xe film in the range of 0,40 monolayers. The penetration depths of the primary ion He+ through the rare gas films increase in the order Ar,<,Kr,<,Xe. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Formation of binary alloy cluster ions from group-14 elements and cobalt and comparison with solid-state alloys

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2001
Xia Zhang
By using laser ablation on mixtures of transition metal cobalt and group-14 elements, binary alloy cluster anions were produced while no binary alloy cluster cations were detected, and the homocluster cations of group-14 elements appeared at very low abundance. The differences between clustering abilities of germanium, tin and lead with cobalt are described, and the chemical bonds in the binary alloy cluster anions appear to indicate a transition from covalent to metal bonds. The cluster anion [CoPb10], appears in very high abundance (magic number), and an endohedral structure is proposed for this cluster. The cluster anion [CoPb12],, also representing a magic number, probably has an icosahedral structure. Compared with solid-state Co/Ge binary alloys, the compositions of most binary alloy cluster anions are germanium-rich, in which the covalent bonds are predominant. Copyright © 2001 John Wiley & Sons, Ltd. [source]


C20 Carbon Clusters: Fullerene,Boat,Sheet Generation, Mass Selection, Photoelectron Characterization

CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2006
Horst Prinzbach Prof. Dr.
Abstract Electron-impact ionization in a time-of-flight mass spectrometer of C20H0,3Br14,12 probes,secured from C20H20 dodecahedrane by a "brute-force" bromination protocol,provided bromine-free C20H0,2(3) anions in amounts that allowed the clean mass-separation of the hydrogen-free C20, ions and the photoelectron (PE) spectroscopic characterization as C20 fullerene (electron affinity (EA)=2.25±0.03 eV, vibrational progressions of 730±70). The extremely strained C20 fullerene ions surfaced as kinetically rather stable entities (lifetime of at least the total flight time of 0.4 ms); they only very sluggishly expel a C2 unit. The HOMO and LUMO are suggested to be almost degenerate (,E=0.27 eV). The assignment as a fullerene was corroborated by the PE characterization of the C20 bowl (EA=2.17±0.03 eV, vibrational progression of 2060±50 cm,1) analogously generated from C20H10 corannulene (C20H1,3Br9,8 samples) and comparably stable. Highly resolved low-temperature PE spectra of the known C20 ring (EA=2.49±0.03 eV, vibrational progressions 2022±45 and 455±30 cm,1), obtained from graphite, display an admixture of, most probably, a bicyclic isomer (EA=3.40±0.03 eV, vibrational progression 455±30 cm,1). The C20+(,) and C20H2+(,) cluster ions generated from polybrominated perylene (C20H0,2Br12,10) have (most probably) retained the planar perylene-type skeleton (sheet, EA=2.47±0.03 eV, vibrational progressions of 2089±30 and 492±30 cm,1 and EA=2.18±0.03 eV, vibrational progressions of 2105±30 and 468±30 cm,1). [source]