<Superscript>57</Superscript>Fe Mössbauer study of the chainpur meteorite

The Chainpur meteorite is one of 23 ordinary chondrites classified as LL3-type (low-Fe & low-metal). It was observed as a shower of stones falling on May 9, 1907 in Uttar Pradesh, India. We report here the characterization of the Fe-bearing phases in this chondrite using ⁵⁷Fe Mössbauer spectroscopy carried out at 298 K, 120 K, 50 K and 13 K. The paramagnetic doublets of olivine and pyroxene dominate the room temperature spectrum, accounting for around 70 % of the spectral area. Moreover, a doublet present with a spectral area of 5 % and assigned to a superparamagnetic Fe ³⁺ phase is a consequence of terrestrial weathering. On the basis of the measured ⁵⁷Fe electric quadrupole splitting of the olivine component at room temperature we estimate the mean Fe:Mg ratio in this meteoritic olivine to be around 35:65 % although there is clearly a wide range of composition. The effects of magnetic ordering of the major components olivine and pyroxene are observed at 13 K.     

Cyclic Elimination and Intramolecular Insertion Reactions of Thermally-Generated Monomeric Metaphosphoric Esters (Metaphosphates)

Abstract

2-Aryl-1,3,2-dioxaphospholanes (aryloxyphosphites) decompose thermally in the gas phase with loss of ethylene to generate aryl metaphosphates which cyclise by intramolecular insertion (phosphonylation) or abstract a β-hydrogen to form a terminal alkene by loss of HPO₃.     

Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

155Gd Mössbauer investigation of the magnetic order and spin-reorientation in Gd3Ag4Sn4

In a recent study of the magnetic order in Gd₃Ag₄Sn₄ by neutron powder diffraction and ¹¹⁹Sn Mössbauer Spectroscopy we showed that both the Gd(2d) and Gd(4e) sublattices order antiferromagnetically at 28.8(2) K. We also demonstrated that the ‘magnetic event’ around 8 K is in fact a ‘plane to axis’ spin-reorientation of the Gd magnetic structure. Here, we extend our study with ¹⁵⁵Gd Mössbauer Spectroscopy. The initial magnetic ordering at 30(2) K is clear for both sites and substantial changes in the hyperfine fields are observed at 8 K when the magnetic structure reorients.     

The numerical integration of relative equilibrium solutions. The nonlinear Schrodinger equation

We analyse different error propagation mechanisms for conservativeand nonconservative time-integrators of nonlinear Schrödingerequations. We use a geometric approach based on interpretingwaves as relative equilibria.