Spectroscopy abundance, clusters

Low resolution spectroscopy, by comparison, has the advantage of providing discrimination against cluster non-members through the use of radial velocities, and can still reach large samples of reasonably faint objects. Common metallicity indicators from low resolution work are Fe and Fe-peak blends, CN, and the Ca II infrared triplet, which are calibrated against high-resolution abundance analyses. 

Ultimately, however, one seeks abundances from high-resolution spectroscopy, and a full elemental abundance analysis. Data on a broad range of elemental abundances in open clusters have been limited until recently. Fortunately, this situation is beginning to change. 

Abstract. A review is presented on abundance determinations in stars of the Galactic bulge, both in the field and in globular clusters. Previous low-resolution spectroscopy results are revised. Recent high resolution and high S/N spectroscopy results based on Keck-Hires, Gemini-Phoenix and VLT-UVES data are presented. Finally, recent analyses of FLAMES data are discussed. 

The jellium model of the free-electron gas can account for the increased abundance of alkali metal clusters of a certain size which are observed in mass spectroscopy experiments. This occurrence of so-called magic numbers is related directly to the electronic shell structure of the atomic clusters. Rather than solving the Schrodinger equation self-consistently for jellium clusters, we first consider the two simpler problems of a free-electron gas that is confined either within a sphere of radius, R, or within a cubic box of edge length, L (cf. problem 28 of Sutton (1993)). This corresponds to imposing hard-wall boundary conditions on the electrons, namely... 

In 1984. scientists (Rohlling. Cox. and Caldor at Exxon Research and Engineering) created clusters of carbon (soot) by the laser vaporization of a carbon target rod in connection with a supersonic nozzle. By means of mass spectroscopy, the researchers determined the relative abundance of the carbon clusters produced. Small, 20- to 40-atom clusters of carbon were expected inasmuch as these had been produced a number of times by earlier investigators working on the soot problem. In such experiments, an interesting but unexplained question always arose—Why were only even-numbered carbon clusters produced in the complete absence of odd-numbered clusters See Fig. 3. 

Spectroscopy and computer simulation have given an abundance of information regarding solvent/solute clustering (3-8). In fact, it is reasonably... 

Two-dimensional exchange spectroscopy might also be a valuable tool in the study of the metal skeleton. No example has been found in the literature. Preferably for nuclei with 100% natural abundance, homonuclear COSY or double-quantmn filtered (DQF)-COSY spectra can give the connectivity pattern of the different metal atoms in a cluster. This holds even, in some cases, for quadnipolar nuclei such as Co [21]. 

As beautiful as this suggestion might be, significantly more must be done to confirm it than to observe that the combination of sixty carbon atoms can be produced in greater abundance than other numbers. Unfortunately, the laser vaporization supersonic cluster beam technique does not produce enough material to perform direct structural techniques like x-ray crystallography or even indirect (but often decisive) experiments such as infrared or Raman spectroscopy, or nuclear magnetic resonance. 

NMR data - The " N nucleus (natural abundance 99.6%, spin 1) is NMR active, but it is a quadrupolar nucleus. Therefore, when it is lodged in unsymmetrical environments, it gives rise to very broad NMR signals. For this reason, the routine N NMR spectroscopy of nitrides is impossible and the data are obtainable only for very symmetrical clusters. The " N NMR spectra have been obtained for the prismatic [M6N(CO)i5] anion (M == Co and Rh, D3h symmetry) and for [RuioN(CO)24], (Td symmetry), whose spectrum consists of a singlet at d 30 (referenced to MeN02, ivi 2 = 21 Hz). This chemical shift, when referenced to NH3, corresponds to 413 ppm and should be compared with the data in the following discussion, since the shifts of N and N are interchangeable. ... 

Aluminum clusters have been investigated using a variety of experimental techniques, providing abundance spectra [164, 165], spin multiplicities [166], IPs [164, 167], EAs, and static polarizability [105]. Reactivity studies have been reported for size-selected A1 clusters in contact with a variety of small molecules (see, for instance, [167]), and the presence of different isomers in a population of clusters has been investigated by measuring the mobility of clusters in a buffer gas [168]. Finally, the electronic structure of these clusters has been probed by photoelectron spectroscopy on the anion species Al [169, 170]. As mentioned above, bulk aluminum is remarkably close to a nearly... 

The Raman investigations on the structure of water-nonaqueous mixed solvents have been quite abundant from 1981 [41,312-325]. The effect of a cosolvent over the water hydrogen-bonded network as well as the formation of clusters and the hydrophobic hydration have been some of the matters studied. When an electrolyte is dissolved in a mixed solvent, some phenomena can be approached by means of Raman spectroscopy. In addition to the change in the extent of the ionic association promoted by the presence of a nonisodielectric cosolvent, which could be interesting for practical purposes [209], the preferential solvation can also be studied. Preferential or selective ion solvation occurs when the first solvation sphere around the cation and/or the anion has a different composition from that corresponding to the bulk mixed solvent [326-329]. 

Nicotinic acid hydroxylase. Nicotinic acid hydroxylase consists of four dissimilar subunits and occurs in forms with different molecular masses. There are 5-7 Fe, one FAD, and one molybdenum molybdopterin per 160 kDa protein. Unusually, nicotinic acid hydroxylase as isolated from Clostridium barkeri contains Mo(V) rather than Mo(VI). By EPR spectroscopy of the enzyme containing either natural-abundance Se or Se (/ = Gladyshev and co-workers showed that Se is directly coordinated, although in an unidentified form to Mo. Furthermore, a flavin radical and two [2Fe-2S] clusters could be observed with EPR spectroscopy. ... 

Another sophisticated way of correlating spins with one another is possible by multiquantum spectroscopy, which can in principle resolve the connectivities of atoms that are present as an isolated cluster. Various multiple-pulse experiments have been designed to recouple isolated spins under fast MAS via multiquantum (or zero-quantum) coherences. When faced with an abundant network of H, however, it is usually only feasible to monitor buildup rates qualitatively as a measure of the dipolar coupling strength. For example, when molecular motion reduces this interaction in polymers, the signal Intensities after quantum production can be interpreted in terms of the respective local dynamics. 

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