Kazuki Furukawa

Infrared photodissociation spectroscopy of Co+(NH3)n and Ni+(NH3)n: preference for tetrahedral or square-planar coordination

Coordination structures of the Co(+)(NH(3))(n) and Ni(+)(NH(3))(n) ions are probed by infrared (IR) photodissociation spectroscopy with the aid of density functional theory (DFT) calculations. The IR spectra of N(2)-tagged Co(+)(NH(3))(n) (n = 1-4) exhibit two distinct bands assignable to the symmetric and antisymmetric NH stretches of the NH(3) molecules binding directly to Co(+). Size-dependent changes in the spectra of Co(+)(NH(3))(n) (n = 4-8) indicate that the first shell of Co(+) is filled with four NH(3) molecules and the resulting 4-coordinated structure forms the central core of further solvation. The spectra of Ni(+)(NH(3))(n) (n = 3-8) suggest that the coordination number of Ni(+) is also four, although a minor 3-coordinated isomer is identified for Ni(+)(NH(3))(4). Despite the same coordination number, the DFT calculations predict a distorted square-planar coordination for Ni(+)(NH(3))(4) and a distorted tetrahedral coordination for Co(+)(NH(3))(4). The coordination of Ni(+)(NH(3))(4) is explainable by using a simple model based on the geometry of a half-filled 3d orbital in Ni(+). This suggests that the Ni(+) ion gives priority to the minimization of the metal-ligand repulsion in accommodating four ligands in the first shell. On the other hand, the same model fails to explain the coordination of Co(+)(NH(3))(4). An interpretation for this is that the Co(+) ion gives priority to the minimization of the ligand-ligand repulsion.

Brownian motion probe for water-ethanol inhomogeneous mixtures

Brownian motion provides information regarding the microscopic geometry and motion of molecules, insofar as it occurs as a result of molecular collisions with a colloid particle. We found that the mobility of polystyrene beads from the Brownian motion in a water-ethanol mixture is larger than that predicted from the liquid shear viscosity. This indicates that mixing water and ethanol is inhomogeneous in micron-sized probe beads. The discrepancy between the mobility of Brownian motion and liquid mobility can be explained by the way the rotation of the beads in an inhomogeneous viscous solvent converts the translational movement.

Influence of Internal Magnetic Field Distribution on Critical Currents in a Single and Assembled Bi-2223 Tapes

We have investigated the influence of self-field on the critical current density distribution in a Bi-2223 tape and its effect on the current capacity of an assembled conductor. Critical current of a tape is usually measured by four-probe transport method under self-field. On the other hand, the critical current of an assembled conductor cannot be simply summed because the tape experiences different condition of magnetic field due to the interaction among the tapes. To quantify the situation, it is necessary to clarify first how the critical current of a tape is determined at the self-field and then to consider the interaction among the tapes. In this study, it was found that the distribution of critical current density was largely influenced by local magnetic field inside the tape. The results were quantitatively described by a model considering the position dependence and magnetic field dependence of local critical current density. Using such a quantitative model, we numerically investigated the current capacities of assembled conductors with different arrangements of the tapes.