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151.
Ellis PD Sears JA Yang P Dupuis M Boron TT Pecoraro VL Stich TA Britt RD Lipton AS 《Journal of the American Chemical Society》2010,132(47):16727-16729
We have examined the antiferromagneticly coupled bis(μ-oxo)dimanganese(IV) complex [Mn(2)O(2)(salpn)(2)] (1) with (55)Mn solid-state NMR at cryogenic temperatures and first-principle theory. The extracted values of the (55)Mn quadrupole coupling constant, C(Q), and its asymmetry parameter, η(Q), for 1 are 24.7 MHz and 0.43, respectively. Further, there was a large anisotropic contribution to the shielding of each Mn(4+), i.e. a Δσ of 3375 ppm. Utilizing broken symmetry density functional theory, the predicted values of the electric field gradient (EFG) or equivalently the C(Q) and η(Q) at ZORA, PBE QZ4P all electron level of theory are 23.4 MHz and 0.68, respectively, in good agreement with experimental observations. 相似文献
152.
We generalise the work of Segre (Ann Mat Pura Appl 4(70):1–201, 1965), Cameron et al. (J Algebra 55(2):257–280, 1978), and Vanhove (J Algebr Comb 34(3):357–373, 2011) by showing that nontrivial m-ovoids of the dual polar spaces \(\mathsf {DQ}(2d, q)\), \(\mathsf {DW}(2d-1,q)\) and \(\mathsf {DH}(2d-1,q^2)\) (\(d\geqslant 3\)) are hemisystems. We also provide a more general result that holds for regular near polygons. 相似文献
153.
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155.
Donald S. Bethune Costantino S. Yannoni Mark Hoinkis Mattanjah de Vries Jesse R. Salem Mark S. Crowder Robert D. Johnson 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):153-158
Fullerenes containing metal atoms and clusters can be formed by the arc-vaporization method. The electronic structure of these metallofullerenes can be probed using magnetic resonance techniques. Electron paramagnetic resonance (EPR) spectra of LaC82, YC82, ScC82 and Sc3C82 have been obtained. Metallofullerenes containing a single metal atom (MC82 with M = La, Y, or Sc), have small hyperfine couplings and g-values close to 2, implying that they can be described as + 3 metal cations within — 3 fullerene radical anion cages. In the La and Y cases, additional EPR active MC82 species have been found. The EPR spectrum of Sc3C82 shows that the metal atoms are equivalent, suggesting that they may form a triangular molecule. No EPR spectrum is found for Y2C82 or for Sc2C2n species (with 2n = 82,84,86), suggesting that they are diamagnetic. Sc NMR spectra of a solution containing Sc2C2n species have been obtained which confirm the diamagnetism of the discandium metallofullerenes. 相似文献
156.
Kroll JH Donahue NM Cee VJ Demerjian KL Anderson JG 《Journal of the American Chemical Society》2002,124(29):8518-8519
Gas-phase ozone-alkene reactions are known to produce the hydroxyl radical (OH) in high yields. Most mechanistic studies to date have focused on the role of syn carbonyl oxides; however, OH production from ethene ozonolysis indicates a second, poorly understood OH-forming channel, which may contribute to OH production in the ozonolysis of substituted alkenes as well. Using laser-induced fluorescence, we have measured OH and OD yields from the ozonolysis of two partially deuterated alkenes, cis- and trans-3-hexene-3,4-d2. OD is formed from both alkenes, indicating a pathway of hydroxyl-radical formation involving vinylic hydrogens, accounting for one-third of total OH formation from cis-3-hexene. The lack of a significant kinetic isotope effect suggests this pathway is the "hot acid" channel, arising from rearrangement of anti carbonyl oxides. Measured yields also allow for the estimation of syn:anti carbonyl oxide ratios, approximately 50:50 for trans-3-hexene and approximately 20:80 for cis-3-hexene, qualitatively consistent with our understanding of ozonide decomposition pathways. 相似文献
157.
Naab FU Holland OW Duggan JL McDaniel FD 《The journal of physical chemistry. B》2005,109(4):1415-1419
The utility of ion beam analysis (IBA) techniques to quantitatively determine impurities in carbon nanotubes (CNTs) over a wide range of atomic numbers is demonstrated. Such techniques have not previously been used to monitor impurities and their effects in this unique material. Despite the difficulty in mounting the samples (which generally are formed into a powdery aggregate rather in a thin film), it is shown that reliable and accurate measurements of impurity concentrations can be achieved. Particle-induced X-ray emission (PIXE) and elastic recoil detection (ERD) analyses were used to characterize both metallic and very light (e.g., hydrogen) impurities in CNTs. This paper reports the first direct measurement of hydrogen in CNTs using an IBA technique. This is significant because CNTs are being actively investigated for hydrogen storage technology for energy applications. 相似文献
158.
H.JesseWalker 《中国科学B辑(英文版)》2001,(Z1)
River mouth areas provide one of the most desired locations for human habitation. Although occupying only a small portion of the total length of the world's shoreline, river mouths are dynamic and complex with highly variable physical and chemical characteristics.The size, shape, and position of a river's mouth are dependent on its geologic and hydrologic history. Further, the processes that operate in a river's mouth are affected by the sea and its currents, tides, and salinity; the river and its discharge and sediment characteristics; and wind generated waves and storm surges. Present-day locations are, geologically speaking, of recent origin because of the rise in sea level that accompanied deglaciation and the sedimentation that followed drowning. 相似文献
159.
H. Jesse Walker 《中国科学B辑(英文版)》2001,44(1):10-22
River mouth areas provide one of the most desired locations for human habitation. Although occupying only a small portion of the total length of the world’s shoreline, river mouths are dynamic and complex with highly variable physical and chemical characteristics.The size, shape, and position of a river’s mouth are dependent on its geologic and hydrologic history. Further, the processes that operate in a river’s mouth are affected by the sea and its currents, tides, and salinity; the river and its discharge and sediment characteristics; and wind generated waves and storm surges. Present-day locations are, geologically speaking, of recent origin because of the rise in sea level that accompanied deglaciation and the sedimentation that followed drowning. 相似文献
160.