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Martin F. Jarrold - One of the best experts on this subject based on the ideXlab platform.
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modeling ionic mobilities by scattering on electronic density isosurfaces application to Silicon Cluster anions
Journal of Chemical Physics, 2000Co-Authors: Alexandre A Shvartsburg, Martin F. Jarrold, Kaiming HoAbstract:We have developed a new formalism to evaluate the gas-phase mobility of an ion based on elastic scattering on an electronic density isosurface (SEDI). In this method, the ion is represented by a surface of arbitrary shape defined as a set of points in space where the total electron density assumes a certain value. This value is the only adjustable parameter in the model. Conceptually, this treatment emulates the interaction between a drifting ion and the buffer gas atoms closer than the previously described methods, the exact hard spheres scattering (EHSS) model and trajectory calculations, where the scattering occurs in potentials centered on the nuclei. We have employed EHSS, trajectory calculations, and SEDI to compute the room temperature mobilities for low-energy isomers of Sin (n⩽20) cations and anions optimized by density functional theory (DFT) in the local density approximation and generalized gradient approximation. The results produced by SEDI are in excellent agreement with the measurements fo...
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high resolution ion mobility measurements for Silicon Cluster anions and cations
Journal of Chemical Physics, 1999Co-Authors: Robert R Hudgins, Martin F. Jarrold, Motoharu Imai, Philippe DugourdAbstract:High-resolution ion mobility measurements have been performed for Silicon Cluster anions and cations, Sin− and Sin+, n=6–55. New isomers have been resolved for every Cluster size larger than Si20. The results for the anions and the cations have the same global features. However, changing the charge often causes a shift in the isomer distribution, or causes new isomers to emerge. For example, the transition from prolate geometries to more-spherical ones is shifted to larger Cluster sizes for the anions than for the cations. The mobilities of the anions are systematically smaller than those of the cations, presumably because of differences in the exterior electron densities.
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mobilities of Silicon Cluster ions the reactivity of Silicon sausages and spheres
Journal of Chemical Physics, 1992Co-Authors: Martin F. Jarrold, Eric J BowerAbstract:The mobilities of size selected Silicon Cluster ions, Si+n (n=10–60), have been measured using injected ion drift tube techniques. Two families of isomers have been resolved by their different mobilities. From comparison of the measured mobilities with the predictions of a simple model, it appears that Clusters larger than Si+10 follow a prolate growth sequence to give sausage‐shaped geometries. A more spherical isomer appears for Clusters with n>23, and this isomer completely dominates for unannealed Clusters with n>35. Annealing converts the sausage‐shaped isomer into the more spherical form for n>30. Activation energies for this ‘‘sausage‐to‐sphere’’ structural transition have been estimated for several Cluster sizes and are ∼1.2–1.5 eV. We have examined the chemical reactivity of the sausages and spheres towards both C2H4 and O2. With C2H4 large differences in reactivity of the isomers were found, with the spherical isomer often being more reactive than the sausage form by more than an order of magnit...
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Annealing of Silicon Clusters
Journal of the American Chemical Society, 1992Co-Authors: Martin F. Jarrold, E. C. HoneaAbstract:Cluster growth often occurs by sequential addition of atoms, a process which may not result in the lowest energy geometric structure. In this paper we describe experimental methods that have been developed to anneal the Clusters, estimate activation energies for annealing, and estimate the relative stabilities of the isomers. The effects of annealing were investigated using the chemical reactivity of the Clusters as a probe. Annealing does not appear to dramatically alter the structure of Silicon Cluster ions containing up to 50 atoms, but changes the relative abundances of the structural isomers that are present. For some Clusters the more reactive isomer is the more thermodynamically stable and its relative abundance increases as these Clusters are annealed. This indicates that the chemical reactivity of the Silicon Clusters is not related to their thermodynamic stability. For the larger Clusters studied (n>25) the estimated activation energies for interconversion between the different structural isomers are between 1.0 and 1.5 eV and do not vary systematically with Cluster size. It was not possible to anneal most of the Clusters to a single structure, suggesting that there are only small differences between the stabilities of the isomers. The stability differences, estimated from the experimental results,more » are typically {approximately}0.2 eV. 27 refs., 6 figs., 3 tabs.« less
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Properties of deposited size‐selected Clusters: Reactivity of deposited Silicon Clusters
The Journal of Chemical Physics, 1992Co-Authors: J. Eric Bower, Martin F. JarroldAbstract:The room temperature oxidation of deposited size‐selected Silicon Clusters (Sin, n=10, 13, and 40–50) has been examined using x‐ray photoelectron spectroscopy (XPS). The size‐selected Clusters were deposited as positive ions on an amorphous carbon substrate at 5 eV. Silicon Cluster sticking probabilities (determined from Rutherford backscattering measurements) were 95%±5%. XPS spectra were recorded both before and after exposure to O2. The unoxidized Clusters showed no significant (≥0.2 eV) core levels shifts relative to bulk Silicon. Oxygen adsorption was monitored by following the evolution of the O1s and Si2p core levels. While the results are qualitatively similar to those obtained for bulk Silicon surfaces, the O2 sticking coefficients are much smaller (∼0.001 compared to ∼0.1). The O2 sticking coefficients are similar to those observed for the larger Clusters in the gas phase, however, the spectacular variations in the reactivity of the smaller Clusters in the gas phase are not reproduced. All the d...
Vladimir A. Constant - One of the best experts on this subject based on the ideXlab platform.
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Silicon Cluster ions: Evidence for a structural transition.
Physical review letters, 1991Co-Authors: Martin F. Jarrold, Vladimir A. ConstantAbstract:The mobilities of size-selected Silicon Cluster ions in helium have been measured using injected-ion drift-tube techniques. The results suggest that a major structural transition occurs for Clusters with ∼7 atoms. Clusters with up to ∼27 atoms appear to follow a prolate growth sequence, resulting in geometries with 'an aspect ratio estimated to be ∼3. Larger Clusters appear to have more spherical shapes. For annealed Clusters this structural transition occurs over a narrow size range
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Silicon Cluster ions evidence for a structural transition
Physical Review Letters, 1991Co-Authors: Martin F. Jarrold, Vladimir A. ConstantAbstract:The mobilities of size-selected Silicon Cluster ions in helium have been measured using injected-ion drift-tube techniques. The results suggest that a major structural transition occurs for Clusters with \ensuremath{\sim}27 atoms. Clusters with up to \ensuremath{\sim}27 atoms appear to follow a prolate growth sequence, resulting in geometries with an aspect ratio estimated to be \ensuremath{\sim}3. Larger Clusters appear to have more spherical shapes. For annealed Clusters this structural transition occurs over a narrow size range.
David Scheschkewitz - One of the best experts on this subject based on the ideXlab platform.
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Atomically Precise Expansion of Unsaturated Silicon Clusters.
Angewandte Chemie (International ed. in English), 2019Co-Authors: Kinga Leszczynska, Volker Huch, Carsten Präsang, Jan Schwabedissen, Raphael J. F. Berger, David ScheschkewitzAbstract:Small- to medium-sized Clusters occur in various areas of chemistry, for example, as active species of heterogeneous catalysis or as transient intermediates during chemical vapor deposition. The manipulation of stable representatives is mostly limited to the stabilizing ligand periphery, virtually excluding the systematic variation of the property-determining Cluster scaffold. We now report the deliberate expansion of a stable unsaturated Silicon Cluster from six to seven and finally eight vertices. The consecutive application of lithium/naphthalene as the reducing agent and decamethylsilicocene as the electrophilic source of Silicon results in the expansion of the core by precisely one atom with the potential of infinite repetition.
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Stable unsaturated Silicon Clusters (Siliconoids).
Dalton transactions (Cambridge England : 2003), 2018Co-Authors: Yannic Heider, David ScheschkewitzAbstract:Unsaturated Silicon Clusters are key intermediates of Silicon deposition processes from the gas phase, which is reflected in the recently introduced term "Siliconoids" for Silicon rich Clusters with at least one hemispheroidally coordinated vertex. Unlike the case of metalloid Clusters of heavier Group 14 elements, stable homonuclear derivatives containing Silicon have become available just recently. This review summarizes the developments since the first report on a stable unsaturated Silicon Cluster in 2005. The synthesis, structure and reactivity under retention of the unsaturated vertices (i.e. the functionalization) of stable Siliconoids is discussed within the broader context of soluble Zintl anions of Silicon and metalloid Clusters. A structural parameter is introduced as a quantitative measure to characterize the "hemispheroidality" of an unsubstituted vertex of a Siliconoid.
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isolation and versatile derivatization of an unsaturated anionic Silicon Cluster Siliconoid
Angewandte Chemie, 2016Co-Authors: Philipp Willmes, Kinga Leszczynska, Yannic Heider, Kai Abersfelder, Michael Zimmer, Volker Huch, David ScheschkewitzAbstract:The characteristic features of bulk Silicon surfaces are echoed in the related partially substituted-and thus unsaturated-neutral Silicon Clusters (Siliconoids). The incorporation of Siliconoids into more-extended frameworks is promising owing to their unique electronic features, but further developments in this regard are limited by the notable absence of functionalized Siliconoid derivatives until now. Herein we report the isolation and full characterization of the lithium salt of an anionic R5 Si6 -Siliconoid, thus providing the missing link between Silicon-based Zintl anions and Siliconoid Clusters. Proof-of-principle for the high potential of this species for the efficient transfer of the intact unsaturated R5 Si6 moiety is demonstrated by clean reactions with representative electrophiles of Groups 13, 14, and 15.
Daniel M Neumark - One of the best experts on this subject based on the ideXlab platform.
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vibrationally resolved photoelectron spectroscopy of Silicon Cluster anions sin n 3 7
Journal of Chemical Physics, 1998Co-Authors: Travis R Taylor, Gordon R Burton, Daniel M NeumarkAbstract:Photoelectron spectra of Sin− (n=3–7) have been measured at several photodetachment energies. The anions were created using a pulsed discharge source, resulting in considerably colder Clusters than in earlier work. As a result, vibrationally resolved spectra were obtained for larger Clusters and more electronic states than in previous studies of these species, leading to more accurate electron affinities, term energies, and vibrational frequencies for the ground and excited electronic states of the neutral Clusters. The assignments of excited states were aided by ab initio calculations and photoelectron angular distributions.
Kit H Bowen - One of the best experts on this subject based on the ideXlab platform.
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photoelectron spectroscopy of lanthanide Silicon Cluster anions lnsin 3 n 13 ln ho gd pr sm eu yb prospect for magnetic Silicon based Clusters
Journal of the American Chemical Society, 2009Co-Authors: Andrej Grubisic, Haopeng Wang, Kit H BowenAbstract:Photoelectron spectroscopy was utilized to study a variety of LnSin− Cluster anions (Ln = Yb, Eu, Sm, Gd, Ho, Pr; 3 ≤ n ≤ 13). For a particular size n, the measured valence electronic transitions of all these systems fall into either one of two categories, reflecting the influence of the different oxidation states of the lanthanide atoms involved. In one, the spectra of YbSin− and EuSin− are nearly identical to each other, while in the other the spectra of GdSin−, HoSin−, and PrSin− are essentially identical. SmSin− Clusters exhibit an intermediate behavior with smaller Clusters resembling the former category and larger Clusters resembling the latter category. In the intermediate size range, 7 ≤ n ≤ 10, for SmSin− both categories appear to be present, with one matching the EuSin−-like systems and the other HoSin−-like Clusters. The distinction between LnSin− categories strongly correlates with the oxidation state of the particular lanthanide as usually found in its compounds. On the basis of this observat...
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photoelectron spectroscopy of europium Silicon Cluster anions eusin 3 n 17
Journal of Chemical Physics, 2008Co-Authors: Andrej Grubisic, Haopeng Wang, Kit H BowenAbstract:We report the photoelectron spectra of EuSin− Cluster anions (3⩽n⩽17). They reveal dramatic electronic rearrangements over the size range n=10–12. In particular, a marked increase in the adiabatic electron affinity of EuSi12 (2.8eV) compared to its stoichiometric neighbor, EuSi11 (1.9eV), is observed. We propose that a significant geometric reorganization due to the encapsulation of a europium atom occurs in this size range and is responsible for the detected changes in the electronic structure. In light of this interpretation, EuSi12 is the smallest fully endohedral europium-Silicon Cluster.
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photoelectron spectroscopy of chromium doped Silicon Cluster anions
Journal of Chemical Physics, 2005Co-Authors: Weijun Zheng, Michael J Nilles, Dunja Radisic, Kit H BowenAbstract:The photoelectron spectra of chromium-doped Silicon Cluster anions, CrSin−, were measured over the size range, n=8–12. Their vertical detachment energies were measured to be 2.71, 2.88, 2.87, 2.95, and 3.18eV, respectively. Our results support theoretical calculations by Khanna, Rao, and Jena [Phys. Rev. Lett. 89, 016803 (2002)] which found CrSi12 to be an enhanced stability (magic) Cluster with its chromium atom encapsulated inside a Silicon cage and with its magnetic moment completely quenched by the effects of the surrounding cage.