Scientific Publications 2006
2006. "Reduction of Uranyl in the Interlayer Region of Low Iron Micas Under Anoxic and Aerobic Conditions." Environmental Science and Technology 40(16):5003-5009. Abstract The role of the interlayer region of three different FeII poor micas (2.8, ~0.02, and 0.01 FeII atom %) on reduction of UVI was investigated at pH ~4.3, low ionic strength, and 23OC under both anoxic and aerated conditions in batch reactors for 1 to 10 days. U diffusion profiles were mapped with X-ray microscopy and the oxidation state of U was tracked with XANES as a function of distance from the crystal edge. Peak U concentrations only reached about 0.006-0.0002 atom percent, where the full-width-at-half-maximums of the diffusion fronts were roughly 25-50 m. Results for anoxic conditions indicated appreciable reduction of uranyl in all three micas with no measurable dependency on distance from the edge. Under aerobic (open to the atmosphere) conditions, U was still partially reduced, although to a lesser degree than for anoxic conditions, and UVI/Utot decreased with time. It is likely that measurable reduction occurred, despite low FeII, because U concentrations were even lower, where FeII/U ratios ranged from about 104-102. A coupled diffusion-reduction model was developed that successfully simulated the proximal portion of the diffusion front. The results show that reduction of UVI in the interlayer of low FeII micas is, in principle, viable and that under aerobic conditions reduction is initially faster than reoxidation. This extends the range of possible environments where heterogeneous reduction of UVI by micas might occur.
2006. "A QM/MM Study on the Aqueous Solvation of theTetrahydroxouranylate [UO₂(OH)₄]²⁻ Complex Ion." Journal of Computational Chemistry 27(11):1156-1162. doi:10.1002/jcc.20434 Abstract We report a QM augmented QM/MM study on the coordination of the tetrahydroxouranylate ion in aqueous solution. QM/MM geometry optimizations followed by full QM single-point calculations on the optimized structures show that a hexa-coordinated structure is more stable than the hepta-coordinated structure by 43 kJ/mol. Charge transfer of the tetrahydroxouranylate to the solvating water molecules is relatively modest, and can be modeled by including a solvation layer consisting of 12 explicit water molecules.
2006. "On the performance of the intermediate Hamiltonian Fock-space coupled-cluster method on linear triatomic molecules: The electronic spectra of NpO₂+, NpO₂ ²+, and PuO₂ ²+. ." Journal of Chemical Physics 125(7):074301 (1-9). doi:10.1063/1.2244564 Abstract The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. In this paper we explore the use of the novel relativistic intermediate Hamiltonian Fock-space coupled-cluster method in the calculation of the electronic spectrum for small actinyl ions (NpO₂+, NpO₂ ²+, and PuO₂ ²+). It is established that the method, in combination with uncontracted double-zeta quality basis sets, yields excitation energies in good agreement with experimental values, and better than those obtained previously with other theoretical methods. We propose the reassignment of some of the peaks that were observed experimentally, and confirm other assignments.
2006. "The C60 Formation Puzzle “Solved”: QM/MD Simulations Reveal the Shrinking Hot Giant Road of the Dynamic Fullerene Self-Assembly Mechanism." Journal of Physical Chemistry B 110:14531-14545. doi:10.1021/jp061173z Abstract An abstract for this journal article is not available at this time.
2006. "Theory and experiment agree: Single-walled carbon nanotube capsgrow catalyst-free with chirality preference on a SiC surface." Journal of Chemical Physics 125:044702. Abstract An abstract for this journal article is not available at this time.