Collision-induced dissociation processes of Nb4+ and Fe4+: fission vs. evaporation

Journal ArticleDespite the extensive effort devoted to research on gasphase metal clusters, quantitative thermodynamic data on such species are scarce. Such information is key to understanding and predicting the physical and chemical properties of clusters. Presently, bond energies are available primarily for transition metal1 dimers2 and some trimers,3 although ionization potentials have been measured for a broader range of sizes.

Collision-induced dissociation of Fen+ (n=2-10) with Xe: ionic and neutral iron binding energies

Journal ArticleCross sections for collision-induced dissociation (CID) of Fen+ with Xe, 2≤n≤10, are presented. Experiments were performed on a newly constructed guided ion beam mass spectrometer, the design and capabilities of which are described in detail. The single mechanism for dissociation of iron cluster ions is sequential loss of iron atoms with increasing collision energies

Oxidation reactions at variably sized transition metal centers: Fen+ and Nbn+ + O2 (N=1-3)

Journal ArticleCross sections for the reactions of Fen+ and Nbn+ (n = 1-3) with 02 are measured as a function of kinetic energy over a range of 0 to > 10 eV. In all systems, analysis yields insight into the kinetics and thermochemistry of the oxidation processes. Nbn+ reaction with 02 exothermically near the Langevin-Gioumousis-Stevenson close-collision limit, driven by formation of strong NbO+ and NbO bonds. Fen+ are less reactive, although oxidation becomes progressively more facile as the size of the reactant increases from Fe+ to Fe3+

Enhancement of Oxygen Transfer by Design Nickel Foam Electrode for Zinc−Air Battery

This is the final version of the article. Available from Electrochemical Society via the DOI in this record.To develop a long-lifetime metal-air battery, oxygen reduction electrodes with improved mass-transfer routes are designed by adjusting the mass ratio of the hydrophobic polytetrafluoroethylene (PTFE) to carbon nanotubes (CNTs) in nickel foam. The oxygen reduction catalyst MnO2 is grown on the nickel foam using a hydrothermal method. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller analysis are employed to characterize the morphology, crystal structure, chemical composition, and pore structure of the electrodes, respectively. The air electrodes are evaluated using constant-current tests and electrochemical impedance spectroscopy. A PTFE:CNT mass ratio of 1:4–2:1 with 3-mm-thick nickel foam yields the optimal performance due to the balance of hydrophilicity and hydrophobicity. When the electrodes are applied in primary zinc–air batteries, the electrode with a PTFE:CNT mass ratio of 1:4 achieves the maximum power density of 95.7 mW cm−2 with a discharge voltage of 0.8 V at 100 mA cm−2, and completes stable discharge for over 14400 s at 20 mA cm−2.The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (21276134, 21776154) and the National 863 Project (2012AA051203)

Methyl (2Z)-2-(2-fluoro-4-meth­oxy­benzyl­idene)-5-(4-meth­oxy­phen­yl)-7-methyl-3-oxo-2,3-dihydro-5H-[1,3]thia­zolo[3,2-a]pyrimidine-6-carboxyl­ate

The asymmetric unit of the title compound, C24H21FN2O5S, consists of two crystallographically independent mol­ecules. In each mol­ecule, the central dihydro­pyrimidine ring is significantly puckered and adopts a conformation which is best described as an inter­mediate between a boat and a screw boat. The least-squares planes of the dihydro­pyrimidine rings are almost coplanar with the fluoro-substituted benzene rings, making dihedral angles of 9.04 (7) and 6.68 (7)°, and almost perpendicular to the meth­oxy-substituted benzene rings with dihedral angles of 89.23 (7) and 88.30 (7)°. In the mol­ecular structure, S(6) ring motifs are formed by C—H⋯O and C—H⋯S hydrogen bonds. In the crystal, mol­ecules are linked into a three-dimensional network by inter­molecular C—H⋯O and C—H⋯F hydrogen bonds. The crystal structure is further stabilized by a C—H⋯π inter­action

2,3-Dibromo-3-(4-chloro­phen­yl)-1-(2-hy­droxy­phen­yl)propan-1-one

In the title mol­ecule, C15H11Br2ClO2, an S(6) ring motif is formed via an intra­molecular O—H⋯O hydrogen bond. The dihedral angle formed between the chloro- and hy­droxy-substituted benzene rings is 34.10 (15)°. In the crystal, weak inter­molecular C—H⋯O hydrogen bonds link the mol­ecules into chains along the c axis

Theory of monolayers with boundaries: Exact results and Perturbative analysis

Domains and bubbles in tilted phases of Langmuir monolayers contain a class of textures knows as boojums. The boundaries of such domains and bubbles may display either cusp-like features or indentations. We derive analytic expressions for the textures within domains and surrounding bubbles, and for the shapes of the boundaries of these regions. The derivation is perturbative in the deviation of the bounding curve from a circle. This method is not expected to be accurate when the boundary suffers large distortions, but it does provide important clues with regard to the influence of various energetic terms on the order-parameter texture and the shape of the domain or bubble bounding curve. We also look into the effects of thermal fluctuations, which include a sample-size-dependent effective line tension.Comment: replaced with published version, 21 pages, 16 figures include

A Constrained Path Quantum Monte Carlo Method for Fermion Ground States

We propose a new quantum Monte Carlo algorithm to compute fermion ground-state properties. The ground state is projected from an initial wavefunction by a branching random walk in an over-complete basis space of Slater determinants. By constraining the determinants according to a trial wavefunction $|\Psi_T \rangle$, we remove the exponential decay of signal-to-noise ratio characteristic of the sign problem. The method is variational and is exact if $|\Psi_T\rangle$ is exact. We report results on the two-dimensional Hubbard model up to size $16\times 16$, for various electron fillings and interaction strengths.Comment: uuencoded compressed postscript file. 5 pages with 1 figure. accepted by PRL

Graphene Transport at High Carrier Densities using a Polymer Electrolyte Gate

We report the study of graphene devices in Hall-bar geometry, gated with a polymer electrolyte. High densities of 6 $\times 10^{13}/cm^{2}$ are consistently reached, significantly higher than with conventional back-gating. The mobility follows an inverse dependence on density, which can be correlated to a dominant scattering from weak scatterers. Furthermore, our measurements show a Bloch-Gr\"uneisen regime until 100 K (at 6.2 $\times10^{13}/cm^{2}$), consistent with an increase of the density. Ubiquitous in our experiments is a small upturn in resistivity around 3 $\times10^{13}/cm^{2}$, whose origin is discussed. We identify two potential causes for the upturn: the renormalization of Fermi velocity and an electrochemically-enhanced scattering rate.Comment: 13 pages, 4 figures, Published Versio