Mass spectrometry, carbon clusters

Thus it is positioned, that at interaction MoCl with acetylene in not polar mediums there is allocation HCl, downturn of a degree of oxidation of molybdenum and formation metallo-organic nanoclusters. Two distances Mo-Mo are foimd out in these clusters by a method of EXAFS-spectros-copy. Two nonequivalent atoms of chlorine and atom of carbon are available in coordination sphere Mo. The conclusion is made on the basis of results MALDl-TOF of mass-spectrometry, that cluster molybdenum has 12 or the 13-nuclear metal skeleton and its structure can be expressed by formulas [MOj Cl CC oH i)] [MOj3Cl24(C,3H3)]-. 

These workers also investigated eight industrially important high-mass polymers by laser microprobe FTICR. These polymers included PEG 8000, poly(phenylene sulfide) (MW 1.0 x 10 ), poly(vinyl acetate) (MW 6.4 x 10 ), poly(styrene) (MW 2.5 x 10 ), PMMA (MW 4.6 x 10 ), poly(vinyl chloride) (3.7 x 10 ), poly(acrylonitrile) (MW 2.3 x 10 ), and poly(dimethylsiloxane) (MW 4.4 x 10 ). Brenna and Creasy posed the question of whether broadband UV laser microprobe FTICR could be used to identify these polymers, and they also wanted to compare spectra with the more widely used TOF laser microprobe mass spectrometry (LAMMA). Results include the observation of odd-mass ions, carbon clustering (Figure 9.4), stable subunit condensation,... 

Isopropyl group (Section 2 13) The group (CH3)2CH— Isotactic polymer (Section 7 15) A stereoregular polymer in which the substituent at each successive chirality center is on the same side of the zigzag carbon chain Isotopic cluster (Section 13 22) In mass spectrometry a group of peaks that differ in m/z because they incorporate differ ent isotopes of their component elements lUPAC nomenclature (Section 2 11) The most widely used method of naming organic compounds It uses a set of rules proposed and periodically revised by the International Union of Pure and Applied Chemistry... 

The elemental composition, oxidation state, and coordination environment of species on surfaces can be determined by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. Both techniques have a penetration depth of 5-20 atomic layers. Especially XPS is commonly used in characterization of electrocatalysts. One common example is the identification and quantification of surface functional groups such as nitrogen species found on carbon-based catalysts.26-29 Secondary Ion Mass spectrometry (SIMS) and Ion Scattering Spectroscopy are alternatives which are more surface sensitive. They can provide information about the surface composition as well as the chemical bonding information from molecular clusters and have been used in characterization of cathode electrodes.30,31 They can also be used for depth profiling purposes. The quantification of the information, however, is rather difficult.32... 

In 1984 it was observed that, upon laser vaporization of graphite, large carbon-only clusters C with u = 30-190 can be produced [14]. The mass distribution of these clusters was determined by time-of-flight mass spectrometry. Only ions with... 

Part of a mass spectrum for the determination of Fe and Cr contamination in boron nitride contaminated with carbon measured by LIMS is shown in Figure 6.9. The analyte ions 53Cr+ and 54Fe+ due to different masses of isobaric atomic and cluster ions are clearly separated from boron and boron carbide cluster ions as demonstrated in Figure 6.9. Cluster ion formation has been studied by laser ionization mass spectrometry (LIMS) on a boron nitride target.10... 

Mass spectrometric characterization of highly hydrogenated fullerenes showed also that some intermediate products are formed before the cage structure of fulleranes collapses fragmented fulleranes. The name fragmented fullerenes is used when fullerene molecule loses some carbon atoms, thus forming e.g. C58, C56, C54 etc. These molecules can be produced from C60 in the form of atomic clusters in gas phase and were typically observed only by mass spectrometry (Murry et al. 1993 Hathiramani et al. 2000 Dunser et al. 1997). Fragmented fulleranes are stable and could be obtained in bulk amounts, see next section for more details. 

Most analytical studies using FT-ICR mass spectrometry, where ions have been produced inside (or just outside) the analyzer cell, have used lasers as ionization sources. Other than some very limited Cs secondary ion mass spectrometry (SIMS) studies [77], most research utilized direct laser desorption to form various organic [78] and inorganic [79] ions, including metal [80] and semiconductor [81] (including carbon) clusters. More recently matrix assisted laser desorption ionization (MALDI) has been used to form ions of high molecular weight from polymers [82] and many classes of biomolecules [83]. 

The mass determination of ionic species (atomic or polyatomic ions) in mass spectrometry is always a comparative measurement, which means the mass of an ionic species is determined with respect to reference masses of elements (or substances) used for mass calibration. The reference mass is thus acquired from the mass unit (m = In = 1/12) of the mass of the neutral carbon isotope (m = 1.66 X 10 kg). A mass calibration is easy to perform in solid-state mass spectrometry if the sample contains carbon (using carbon cluster ions with whole masses, as discussed above). The so-called doublet method was apphed formerly, e.g., ions and doubly charged Mg + forming a doublet at the same nominal mass number 12 were considered, where they are slightly displaced with respect to one another. The doublet method is no longer of relevance in modern inorganic mass spectrometry. Orientation in the mass spectra can be carried out via the matrix, minor and trace elements after mass calibration and by comparing the measured isotopic pattern of elements with theoretical values. 

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