Formation of Metal Oxyfluorides from Specific Metal Reactions with Oxygen Difluoride: Infrared Spectroscopic and Theoretical Investigations of the OScF2 Radical and OScF with Terminal Single and Triple Sc?O Bonds

The scandium oxydifluoride free radical, OScF₂, is produced by the spontaneous, specific reaction of laser ablated Sc atoms with OF₂ in solid argon and characterized by using matrix infrared spectroscopy and theoretical calculations. The OScF₂ molecule is predicted to have C_2v symmetry and a ²B₂ ground state with an unpaired electron located primarily on the terminal oxygen atom, which makes it a scandium difluoride molecule coordinated by a neutral oxygen atom radical in forming the Sc? O single bond. The closed shell singlet OScF molecule with an obtuse bent geometry has a much shorter Sc? O bond of 1.682 Å than that of the OScF₂ radical (1.938 Å) on the basis of B3LYP calculations. The Sc? O bond in OScF consists of two covalent bonds and a dative bond in which the oxygen 2p_π lone pair donates electron density into an empty Sc 3d orbital thus forming a triple oxo bond. Density functional calculations suggest it is highly exothermic for fluorine transfer from OF₂ to scandium, which favors the formation of the OScF₂ radical species as well as the OScF molecule after fluorine loss.     

Disturbed oscillatory brain dynamics in subcortical ischemic vascular dementia

Background

This study examined the effects of dietary polyunsaturated fatty acids (PUFA) as different n-6: n-3 ratios on spatial learning and gene expression of peroxisome- proliferator-activated receptors (PPARs) in the hippocampus of rats. Thirty male Sprague?CDawley rats were randomly allotted into 3 groups of ten animals each and received experimental diets with different n-6: n-3 PUFA ratios of either 65:1, 22:1 or 4.5:1. After 10?weeks, the spatial memory of the animals was assessed using the Morris Water Maze test. The expression of PPAR?? and PPAR?? genes were determined using real-time PCR.

Results

Decreasing dietary n-6: n-3 PUFA ratios improved the cognitive performance of animals in the Morris water maze test along with the upregulation of PPAR?? and PPAR?? gene expression. The animals with the lowest dietary n-6: n-3 PUFA ratio presented the highest spatial learning improvement and PPAR gene expression.

Conclusion

It can be concluded that modulation of n-6: n-3 PUFA ratios in the diet may lead to increased hippocampal PPAR gene expression and consequently improved spatial learning and memory in rats.     

Strategies for obtaining the maximum performance from current supercomputers

The exploitation of special features of the current generation of supercomputers is discussed with particular reference to computational quantum chemistry. Modification of algorithms in the light of the very large memory available on the CRAY 2 is described, and multi-processing of programs is considered for both the CRAY XMP and CRAY 2. The overhead in multiprocessing can be reduced to a small percentage even for steps that perform extensive IO. The division of work among CPU's at different program levels is considered for various examples, and optimal levels for the division are discussed.     

Barrier height for the abstraction reaction of methylene with hydrogen,CH2(3B1) + H2 → CH3 + H

The abstraction reaction of methylene with hydrogen reinvestigated with a double zeta plus polarization basis at the configuration interaction level. The results are found to be very similar to those previously obtained without polarization functions, in line with previous findings at the SCF level. The barrier is computed to be 11.8 kcal/mole when an estimate of the effect of quadruple excitations is included.     

Molecular structure and properties of CH3BeF and CH3MgF

The molecules methylberyllium fluoride and methylmagnesium fluoride have been studied using a priori electronic structure theory. Self-consistent-field wavefunctions have been computed over a double zeta basis set of contracted gaussian functions. The geometrical structure of each molecule has been predicted assuming the three heavy atoms are collinear. For CH₃ BeF, the predicted C-Be and Be-F distances are 1.70 and 1.40 Å. For CH₃MgF, the analogous bond distances are 2.08 Å and 1.78 Å. A number of molecular properties have been predicted including dipole moments, which are 1.75 and 2.38 debye for CH₃BeF and CH₃MgF.     

Full CI benchmark calculations for molecular properties

Full CI calculations of first- and second-order properties are presented to provide benchmark results for comparisons with other methods, such as multireference CI(MRCI). The full CI(FCI) polarizability of F^– is computed using a double zeta plus polarization plus diffuse basis set. These FCI results are compared to those obtained at other levels of theory; the CASSCF/MRCI with Davidson correction results are in excellent agreement with the FCI. Differences between the polarizability results computed as a (numerical) second derivative of the energy or as an induced dipole moment are also discussed. FCI calculations are presented for the dipole moment and polarizability of HF, CH₂ and SiH₂ using a DZP basis set. Again, the CASSCF/MRCI values are in excellent agreement with the FCI results, whereas SDCI values, whether computed as an expectation value or as an energy derivative, are much worse. The results obtained using the CPF approach are in considerably better agreement with the FCI results than SDCI, and are similar in quality to the SDCI energy derivative results with the inclusion of Davidson's correction.     

What is the structure of FeC5H6?

Calculations performed using both density functional theory (DFT) and the modified coupled-pair functional (MCPF) approach show that FeC₅H₆⁺ is more stable than HFeC₅H₅⁺ by about 10 kcal/mol. The ground state of FeC₅H₆⁺ is a quartet state derived from the 3d⁷ occupation of Fe⁺. For HFeC₅H₅⁺, the MCPF approach yields a sextet ground state while DFT yields a quartet; however, these two states are close in energy at both levels of theory.     

CAS SCF Cl calculations for the 3Σ−g, 1Σ+g, 3Σ+u, and 5Δu states of Sc2

CAS SCF CI (SD) calculations have been carried out for the ³Σ^?_g, ¹Σ⁺_g, ³Σ⁺_u, and ⁵Δ_u states of Sc₂ using large gaussian basis sets. The ³Σ^?_g, ¹Σ⁺_g, and ³Σ⁺_u states arise from the ²D(4s² 3d¹) + ²D(4s² 3d¹) limit of Sc₂ and are found to be only weakly bound (D_c ≈ 0.06 eV and R_c ≈ 8.0a₀). The ⁵Δ_u state arises from the ²D(4s² 3d¹) + ⁴F(4s¹ 3d¹ 4p¹) atomic limit. This state is found to be strongly bound relative to its limits (D_c ≈ 0.8 eV and R_c ≈ 7.0a₀).