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Geometries and stabilities of Ag-doped Sin (n=1-16) clusters: a first-principles studyHsieh, Yun-Yi 01 July 2008 (has links)
The structures of AgSin (n = 1 ¡V 16) clusters are investigated using first-principles calculations.
Our studies suggest that AgSin clusters with n = 7, 10, and 15 are relatively
stable isomers and that these clusters prefer to be exohedral rather than endohedral.
Moreover, doping leaves the inner core structure of the clusters largely intact. Additionally,
the plot of fragmentation energies as a function of silicon atoms shows
that the AgSin are favored to dissociate into one Ag atom and Sin clusters. Alternative
pathways exist for n > 7 (except n = 11 and 16) in which the AgSin cluster dissociates
into a stable Si7 and a smaller fragment AgSin7. The AgSi11 and AgSi16 cluster dissociates
into a stable Si10 and a small fragment AgSi. Lastly, our analysis indicates that
doping of Ag atom significantly decreases the gaps between the highest occupied
molecular orbital and the lowest unoccupied molecular orbital for n > 7.
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Atomic and electronic structures of AuSin(n=1-16) clusters from first-principlesHsu, Chih-chiang 04 February 2009 (has links)
The structures of AuSin (n = 1 - 16) clusters are investigated systematically using first-principles calculations. The lowest energy isomers exhibit preference toward exohedral rather than endohedral structure. Our studies suggest that AuSin clusters with n = 5 and 10 are relatively stable isomers. We found no significant alteration in the cluster¡¦s inner core structure for sizes n= 6, 7, 10, 11, 12, 14, and 15 even in the presence of doping. Moreover, analysis of fragmentation energies is presented in detail. Our studies further indicate that doping of Au atom significantly decreases the gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital for n > 7. Additionally, we report on similar results obtained for CuSin (n = 1 - 16) and AgSin (n = 14, 15, and 16) and compared them with those on AuSin clusters. Next, the low energy isomers for certain sizes of CuSin (n = 10 -16 ) clusters are selected for further optimizations using Gaussian 03 package. We found that for CuSin (n = 12 - 16 ), the endohedral isomers have lower energies than their exohedral counterparts, consistent with a recent study by Janssens et al. [15] in which a similar trend was observed.
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Towards quantum telecommunication and a Thorium nuclear clockRadnaev, Alexander G. 17 August 2012 (has links)
This thesis presents the investigations of Rubidium atoms in magneto-optical traps and triply charged Thorium ions in electrodynamic traps for future advances in long-distance quantum telecommunication, next generation clocks, and fundamental tests of current physical theories. Experimental realizations of two core building blocks of a quantum repeater are described: a multiplexed quantum memory and a telecom interface for long-lived quantum memories. A color change of single-photon level light fields by several hundred nanometers in an optically thick cold gas is demonstrated, while preserving quantum entanglement with a remotely stored matter excitation. These are essential elements for long-distance quantum telecommunication, fundamental tests of quantum mechanics, and applications in secure communication and computation. The first trapping and laser cooling of Thorium-229 ions are described. Thorium-229 nuclear electric quadrupole moment is revealed by hyperfine spectroscopy of triply charged Thorium-229 ions. A system to search for the isomer nuclear transition in Thorium-229 is developed and tested with the excitation of a forbidden electronic transition at 717 nm. Direct excitation of the nuclear transition with laser light would allow for an extremely accurate clock and a sensitive test bed for variations of fundamental physical constants, including the fine structure constant.
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Untersuchung der Bildung, des Isotopenaustausches und der Isomerisierung des Ionensystem HCO+/HOC+Freiherr von Richthofen, Jan 19 August 2002 (has links)
This work is about the reaction around both
isomeres of formylcations, formylcation (HCO+)
and isoformylcation (HOC+). In interstellar
chemistry these isomeres are of significant
importance: radio astronomic measurements have
detected the metastabil isomere HOC+ in present
of the stabil isomere HCO+ in many objects. The
HOC+ was found in photon dominated regions like
(SgrB2, NGC 7538 und NGC 2024) as well as in
dense clouds like DR21 (OH), W51M, W3 (OH),
Orion (3N, 1E)). The ratecoefficiants for
reactions forming both isomeres have been
measured. Further more the ratecoefficiant for
the isomerisation of isoformyl (HOC+) with
molecular hydrogen has been measured at 25 K. / In der vorliegenden Arbeit werden Untersuchungen
zu dem Ionensystem Formylkationen (HCO+) /
Isoformylkationen (HOC+) vorgestellt. In der
interstellaren Chemie kommt diesen Isomeren eine
hohe Bedeutung zu: neuere radioastronomische
Beobachtungen haben das metastabile Ion HOC+ in
Anwesenheit des stabilen Isomers HCO+ in einer
Vielzahl von interstellaren Umgebungen
nachgewiesen. Das HOC+ - Isomer ist in
signifikanter Dichte sowohl in Photon -
dominierten Gebieten (wie z.B. SgrB2, NGC 7538
und NGC 2024) als auch in Dichten Molekularen
Wolken (wie z.B. DR21 (OH), W51M, W3 (OH),
Orion (3N, 1E), Orion KL, und G34.3)
festgestellt worden. Es konnten die
Ratenkoeffizienten für die Bildungsreaktionen
beider Isomere bestimmt werden. Des weiteren
konnte die Isomerisierung von Isoformylkationen
(HOC+) mit Wasserstoff (H2) bei 25 K estimmt
werden.
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Synthesis and Characterization of Surface-Confined Ionic Liquid Stationary Phases for High Performance Liquid ChromatographyVan Meter, David S., III January 2008 (has links)
No description available.
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Sources of dioxins and other POPs to the marine environment : Identification and apportionment using pattern analysis and receptor modelingSundqvist, Kristina January 2009 (has links)
In the studies underlying this thesis, various source tracing techniques were applied to environmental samples from the Baltic region. Comprehensive sampling and analysis of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in surface sediments in Swedish coastal and offshore areas resulted in a unique data set for this region. Nearly 150 samples of surface sediments were analyzed for all tetra- to octa-chlorinated PCDD/Fs. The levels showed large spatial variability with hotspots in several coastal regions. Neither Sweden nor the EU has introduced guideline values for PCDD/Fs in sediment, but comparisons to available guidelines and quality standards from other countries indicate that large areas of primarily coastal sediments may constitute a risk to marine organisms. Multivariate pattern analysis techniques and receptor models, such as Principal Component Analysis (PCA) and Positive Matrix Factorization (PMF), were used to trace sources. These analyses suggested that three to six source types can explain most of the observed pattern variations found in the sediment samples. Atmospheric deposition was suggested as the most important source to offshore areas, thus confirming earlier estimates. However, spatial differences indicated a larger fraction of local/regional atmospheric sources, characterized by PCDFs, in the south. This was indicated by the identification of several patterns of atmospheric origin. In coastal areas, the influence of direct emission sources was larger, and among these, chlorophenol used for wood preservation and emissions from pulp/paper production and other wood related industry appeared to be most important. The historic emissions connected to processes involving chemical reactions with chlorine (e.g. pulp bleaching) were found to be of less importance except at some coastal sites. The analysis of PCDD/Fs in Baltic herring also revealed spatial variations in the levels and pollution patterns along the coast. The geographical match against areas with elevated sediment levels indicated that transfer from sediments via water to organisms was one possible explanation. Fugacity, a concept used to predict the net transport direction between environmental matrices, was used to explore the gas exchange of hexachlorocyclohexanes (HCHs) and polychlorinated biphenyls (PCBs) between air and water. These estimates suggested that, in the Kattegat Sea, the gaseous exchange of HCHs primarily resulted in net deposition while PCBs were net volatilized under certain environmental conditions. The study also indicated that, while the air concentrations of both PCBs and γ-HCH are mostly dependent upon the origin of the air mass, the fluctuations in α-HCH were primarily influenced by seasonal changes.
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