Gaussian-2 (G2) theory has been extended to molecules containing the third-row nontransition elements Ga–Kr. Basis sets compatible with those used in G2 theory for molecules containing first- and second-row atoms have been derived. Spin–orbit corrections for atoms and molecules having spatially degenerate states (2P, 3P for atoms and 2Π for molecules in this work) are included explicitly in the G2 energies. The average absolute deviation from experiment for 40 test reactions is 1.37 kcal/mol. In contrast to the situation for first- and second-row molecules, inclusion of spin–orbit effects is very important in attaining accurate energies for molecules containing third-row atoms. Without spin–orbit effects, the average absolute deviation is 2.36 kcal/mol.

Gaussian-2 (G2) theory has been extended to molecules containing the third-row nontransition elements K and Ca. Basis sets compatible with those used in G2 theory for molecules containing first- and second-row atoms, as well as the third-row elements Ga–Kr, have been derived. As for Ga–Kr, first-order spin–orbit corrections are included explicitly in the G2 energies of K- and Ca-containing atoms and molecules. In contrast to the procedure for Ga–Kr, the 3s and 3p orbitals need to be included in the correlation space for K- and Ca-containing molecules. The geometries obtained with the new basis sets are in satisfactory agreement with experiment. Assessment of the thermochemical predictions is limited because of the sparsity of accurate experimental data for molecules containing K and Ca. Ionization energies are generally in good agreement with experimental values, as are the atomization energies for K-containing molecules. However, there are larger differences between theoretical and experimental atomization energies for Ca-containing molecules.

Insights about the redox speciation of neptunium in an aqueous mineral acid electrolyte were obtained through a combination of in situ EXAFS (extended X-ray absorption fine structure) spectroelectrochemistry, density functional theory (DFT), and simple geometric modeling. A single solution of neptunium in 1 M perchloric acid was used to extract metrical information about the Np coordination environment, in terms of hydration numbers (n) and Np-O interatomic distances. Four aquo ions - Np

Actinyl complexes are shown, on the basis of known theoretical and experimental results, to be weak-field complexes in 4/7 of the 5f orbital space, the other 3/7 of this space being strongly affected by bonding to the -yl oxygens. The interactions present in these complexes are placed in order of size so that a coupling scheme (Λ-S), including the choice of quantum numbers of varying quality, can be specified. Electronic spectra in the near-infrared and visible regions are discussed in general terms, including different choices of both the lower and upper orbitals (or spin−orbitals) involved in the excitations. For the isolated ions, all transitions in this region are forbidden by electric-dipole selection rules, but the interactions with equatorial ligands can make such transitions allowed.

The accelerating effect of anions for electrode reactions has been known for a long time, but it is much less appreciated that these effects can sometimes be caused by traces of anions. We have demonstrated that the Cu § + reaction is strongly catalyzed by trace amounts of chloride ions in the solution. The Cu+/Cu reaction was found to be unaffected by chloride ions. These experimental results were also substantiated by theoretical calculations. We have investigated the electronic coupling for homogeneous electron-transfer reactions that are approximate models for electron transfer in the copper deposition: (i) outer-sphere reaction (water-water bridge), and (fi) innersphere reaction (chloride bridge). For Cu++/Cu+ electron transfer we found increased coupling for the chloride bridge, which we attribute to the closer approach found for this complex compared to the water bridge, while for CuUCu electron transfer, coupling was not increased for the chloride bridge reaction.

The coordination environment of Np(VII) in solution remains uncertain despite numerous studies. Interest in the heptavalent Np ion is driven by the implications of the coordination environment on the basic understanding of structure/bonding relationships and its technological importance in treating nuclear waste. Initially reported by Krot and Gelman in 1967, 1 this f 0 configuration of Np is slowly reduced by H 2 O in strongly alkaline solutions, and rapidly reduced in acidic media. Studies in highly basic solutions have reported various coordination geometries, including the dioxo moiety, OdNpdO, coordinated equatorially to oxo or hydroxo anions or waters, 2,3 and a square planar tetraoxo complex with two more distant axial hydroxide ions. 4 The latter Np(VII) coordination has precedent in the solid state. 5 Analogies with other high-valent actinide ions, including U(VI), Np(VI), and Pu(VI), suggest that the hydroxy neptunyl ion NpO 2 (OH) n (3-n) (H 2 O) m is the prevalent species in solution. In contrast, the oxo anions of hexa-and heptavalent transition metals exhibit tetrahedral MO 4 ncoordination. We report the results of Np L 3 -edge X-ray absorption spectroscopy (XAS) experiments optimized to determine the coordination environments of Np(VI) and Np(VII) in a highly basic solution. The results of these experiments, taken together with density functional theory (DFT) calculations, show Np(VII) to have a tetraoxo coordination with two additional more distant hydroxy ligands or water molecules.An alkaline suspension of Np was prepared by precipitating Np(V) with concentrated NaOH. The resulting Np(V) hydroxide precipitate was slurried with 1 M NaOH and transferred to a purpose-built spectroelectrochemical cell equipped with Pt working and auxiliary electrodes and a Ag/AgCl reference electrode. 6 Np(V) was oxidized, first to Np(VI) and then to Np(VII), by continuously sparging the solution with ozone while simultaneously applying an oxidizing potential of +600 mV vs Ag/AgCl. The standard reduction potential for Np(VII) under the conditions of our experiment has been previously reported as +384 mV. 7 After several hours, the ozone was stopped and the applied potential was reduced to +500 mV. X-ray data were collected 8 on the oxidized Np. The applied potential was reduced and data were obtained after bulk electrolysis at intermediate potentials until the solution contained only Np(VI).The L 3 -edge XANES data obtained from the 6.5 mM Np solution during and after ozonolysis and as a function of applied potential are shown in Figure 1. The Np(VI) spectrum, part d in Figure 1, exhibits the shoulder feature characteristic of an actinyl moiety, 9,10 and is similar to the spectrum of Np(VI) and Np(V) in aqueous acidic solution. 11 In contrast, the spectrum of the Np(VII) species has a broader, doubled white line, thereby suggesting a change in the coordination environment from a simple OdNpdO configuration. The coordination environments of Np(VI) and Np(VII) are quantified by analyses of the EXAFS data and their Fou...

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