Senior Recital:Christopher Keniley, Percussion

Kemp Recital Hall:Saturday Evening December 3, 2005 6:00p.m

Coupling a Boltzmann plasma and BCA surface for the kinetic treatment of plasma-material interactions

A near-wall plasma and material surface form a volatile region involving surface erosion, impurity ionization, and redeposition, creating a far-from-equilibrium system of mutually interacting plasma and impurity species. As impurity recycling is expected to play a major role in the long-term performance of plasma-facing components in magnetic fusion devices, modeling of the plasma- surface interface is required to predict the behavior of both the material surface and the near-wall plasma. In this work, a method of simulating plasma-material interactions by dynamically coupling a continuum Boltzmann plasma model to a Monte-Carlo surface model is presented. The model is based on a multi-species Boltzmann solver for the plasma using finite difference methods. Von Neumann stability analysis of the Runge-Kutta time discretization with upwind-biased numerical schemes are detailed up to fourth-order accuracy, and the errors associated with each scheme are quantified. A modification to the classical binary-collision approximation code TRIDYN is utilized to model the surface, which was treated as a boundary condition to the plasma model. The Boltzmann solver calculates the ion energy-angle distribution and density of ions striking the surface that are needed as input to the BCA code, and density estimation is used to reconstruct a velocity distribution to be passed back to the Boltzmann solver. Both plasma ions and impurities are treated as Boltzmann kinetic species, allowing high resolution even at very disparate densities, particle fluxes, drift velocities, and energy fluxes. The plasma model is shown to be capable of resolving features of Landau damping with matching theoretical and calculated damping rates of 0.1534, and the two-stream instability is shown to have an energy peak at 18 tωp. Convergence of the plasma sheath problem is established utilizing the fourth-order upwind finite difference method. Numerical density estimation techniques are applied to construct velocity distributions from discrete data samples provided by TRIDYN, and a sputtered particle sample size of 1000 is shown to constrain the mean integrated squared error of the density-estimated velocity distribution to O(10^−1). As a proof-of-concept of the coupling method, an example calculation of a helium plasma facing a beryllium wall is reported in both unmagnetized and magnetized conditions, recording the evolution of the phase spaces of ions, neutrals, and material impurities in the near-wall region at nominal ITER conditions

Complexes with Redox-Active Ligands: Synthesis, Structure, and Electrochemical and Photophysical Behavior of the Ru(II) Complex with TTF-Annulated Phenanthroline

Ru(II) complexes with chelating ligands, 4′,5′-ethylenedithiotetrathiafulvenyl[4,5-f][1,10]phenanthroline (L1), 1,3-dithiole-2-thiono[4,5-f][1,10]phenanthroline (L2), and 1,3-dithiole-2-ono[4,5-f][1,10]phenanthroline (L3), have been prepared and their structural, electrochemical, and photophysical properties investigated. Density functional theory (DFT) calculations indicate that the highest occupied molecular orbital of [Ru(bpy)2(L1)](PF6)2 (1) is located on the tetrathiafulvalene (TTF) subunit and appears ≈0.6 eV above the three Ru-centered d orbitals. In agreement with this finding, 1 exhibits three reversible oxidations: the two at lower potentials take place on the TTF subunit, and the one at higher potential is due to the Ru3+/Ru2+ redox couple. Complexes [Ru(bpy)2(L2)](PF6)2 (2) and [Ru(bpy)2(L3)](PF6)2 (3) exhibit only the Ru3+/Ru2+-related oxidation. The optical absorption spectra of all complexes reveal a characteristic metal-to-ligand charge transfer (MLCT) band centered around 450 nm. In addition, in the spectrum of 1 the MLCT band is augmented by a low-energy tail that extends beyond 500 nm and is attributed to the intraligand charge transfer (ILCT) transition of L1, according to time-dependent DFT calculations. The substantial decrease in the luminescence quantum yield of 1 compared to those of 2 and 3 is attributed to the reductive quenching of the emissive state via electron transfer from the TTF subunit to the Ru3+ center, thus allowing nonradiative relaxation to the ground state through the lower-lying ILCT state. In the presence of O2, complex 1 undergoes a photoinduced oxidative cleavage of the central C═C bond of the TTF fragment, resulting in complete transformation to 3. This photodegradation process was studied with 13C NMR and optical absorption spectroscopy

Complexes with Redox-Active Ligands: Synthesis, Structure, and Electrochemical and Photophysical Behavior of the Ru(II) Complex with TTF-Annulated Phenanthroline

Ru­(II) complexes with chelating ligands, 4′,5′-ethylene­dithio­tetra­thiafulvenyl­[4,5-<i>f</i>]­[1,10]­phenan­throline (<b>L1</b>), 1,3-dithiole-2-thiono­[4,5-<i>f</i>]­[1,10]­phenanthroline (<b>L2</b>), and 1,3-dithiole-2-ono­[4,5-<i>f</i>]­[1,10]­phenanthroline (<b>L3</b>), have been prepared and their structural, electrochemical, and photophysical properties investigated. Density functional theory (DFT) calculations indicate that the highest occupied molecular orbital of [Ru­(bpy)₂(<b>L1</b>)]­(PF₆)₂ (<b>1</b>) is located on the tetrathiafulvalene (TTF) subunit and appears ∼0.6 eV above the three Ru-centered d orbitals. In agreement with this finding, <b>1</b> exhibits three reversible oxidations: the two at lower potentials take place on the TTF subunit, and the one at higher potential is due to the Ru³⁺/Ru²⁺ redox couple. Complexes [Ru­(bpy)₂(<b>L2</b>)]­(PF₆)₂ (<b>2</b>) and [Ru­(bpy)₂(<b>L3</b>)]­(PF₆)₂ (<b>3</b>) exhibit only the Ru³⁺/Ru²⁺-related oxidation. The optical absorption spectra of all complexes reveal a characteristic metal-to-ligand charge transfer (MLCT) band centered around 450 nm. In addition, in the spectrum of <b>1</b> the MLCT band is augmented by a low-energy tail that extends beyond 500 nm and is attributed to the intraligand charge transfer (ILCT) transition of <b>L1</b>, according to time-dependent DFT calculations. The substantial decrease in the luminescence quantum yield of <b>1</b> compared to those of <b>2</b> and <b>3</b> is attributed to the reductive quenching of the emissive state via electron transfer from the TTF subunit to the Ru³⁺ center, thus allowing nonradiative relaxation to the ground state through the lower-lying ILCT state. In the presence of O₂, complex <b>1</b> undergoes a photoinduced oxidative cleavage of the central CC bond of the TTF fragment, resulting in complete transformation to <b>3</b>. This photodegradation process was studied with ¹³C NMR and optical absorption spectroscopy

Heteroleptic FeII Complexes of 2,2′-Biimidazole and Its Alkylated Derivatives: Spin-Crossover and Photomagnetic Behavior

Three iron(II) complexes, [Fe(TPMA)(BIM)](ClO4)2⋅0.5H2O (1), [Fe(TPMA)(XBIM)](ClO4)2 (2), and [Fe(TPMA)(XBBIM)](ClO4)2 ⋅0.75CH3OH (3), were prepared by reactions of FeII perchlorate and the corresponding ligands (TPMA=tris(2-pyridylmethyl)amine, BIM=2,2′-biimidazole, XBIM=1,1′-(α,α′-o-xylyl)-2,2′-biimidazole, XBBIM=1,1′-(α,α′-o-xylyl)-2,2′-bibenzimidazole). The compounds were investigated by a combination of X-ray crystallography, magnetic and photomagnetic measurements, and Mössbauer and optical absorption spectroscopy. Complex 1 exhibits a gradual spin crossover (SCO) with T1/2=190 K, whereas 2 exhibits an abrupt SCO with approximately 7 K thermal hysteresis (T1/2=196 K on cooling and 203 K on heating). Complex 3 is in the high-spin state in the 2–300 K range. The difference in the magnetic behavior was traced to differences between the inter- and intramolecular interactions in 1 and 2. The crystal packing of 2features a hierarchy of intermolecular interactions that result in increased cooperativity and abruptness of the spin transition. In 3, steric repulsion between H atoms of one of the pyridyl substituents of TPMA and one of the benzene rings of XBBIM results in a strong distortion of the FeII coordination environment, which stabilizes the high-spin state of the complex. Both 1 and 2 exhibit a photoinduced low-spin to high-spin transition (LIESST effect) at 5 K. The difference in the character of intermolecular interactions of 1 and 2 also manifests in the kinetics of the decay of the photoinduced high-spin state. For 1, the decay rate constant follows the single-exponential law, whereas for 2 it is a stretched exponential, reflecting the hierarchical nature of intermolecular contacts. The structural parameters of the photoinduced high-spin state at 50 K are similar to those determined for the high-spin state at 295 K. This study shows that N-alkylation of BIM has a negligible effect on the ligand field strength. Therefore, the combination of TPMA and BIM offers a promising ligand platform for the design of functionalized SCO complexes