Spin frustration and concealed asymmetry: structure and magnetic spectrum of [Fe3O(O2CPh)6(py)3]ClO4·py

The oxo-centred trinuclear complex [Fe3O(O2CPh)(6)(py)(3)]ClO4. py and its fully deuteriated analogue have been synthesized. X-Ray crystallography at T=233 K shows that the complex has threefold symmetry, space group P6(3)/m. Incoherent inelastic neutron scattering spectra at T=1.5 K however show the presence of two inequivalent sets of molecules, one a static "isosceles" coupled system, with two J values for the three metal-metal interactions, the other a dynamic system, with rapid pseudorotation between equivalent isosceles geometries. Combining infrared and neutron scattering data, the distortion of the cluster has been estimated

Dynamical structure of methane hydrate by neutron inelastic scattering

中性子が物質中の原子や分子の熱運動程度のエネルギーを持つと，その波長は原子サイズのオーダー になる．これにより，Ｘ線の回折と同様な条件の下，凝集体の回折現象の測定が可能となるうえ，原 子・分子の熱運動と中性子の間のエネルギーのやり取りを観測しやすい．つまり，中性子散乱実験で は，凝集体の空間的な構造と運動に関する情報，すなわち動的構造を一挙に得ることが可能となる． ここでは，この中性子散乱測定の特長を活かしてメタンハイドレートの測定を行い，得られた３次元 的な構造を持つスペクトルからメタン分子の微視的な運動を詳細に解析した例を示す．Clathrate hydrates are nonstoichiometric inclusion compounds with a host framework composed of water molecules. Methane hydrate consists of two kinds of water cages, two pentagonal dodecahedra and six tetrakaidecahedra in a unit cell,which contains one methane molecule in each. It has been said that the methane molecule rotates almost free in the cage. We made measurements of dynamical structure factors over the wide Q-E space using neutron inelastic scattering. The obtained dynamical structure factor S(Q,E) of methane hydrate shows a characteristic feature in Q-E space. The rotational levels of methane coincide with those of a free methane molecule and show a recoil like behavior in the high Q region, meaning that methane molecules in methane hydrate rotate almost freely.3章 クラスレートハイドレート研究のフロンティ

Structure and Dynamics of Molecular Hydrogen in the Interlayer Pores of a Swelling 2:1 Clay by Neutron Scattering

Neutron scattering has been used to reveal the structure and dynamics of molecular H₂ physisorbed into the two-dimensional pores of sparingly hydrated Ca-laponite clay. Thermal pretreatment of the clay at 415 K under vacuum yielded an interlayer composition in the 1.0–1.5 water molecules per Ca²⁺ cation range and provided a vacant gallery height of 2.82 Å. This value is very well matched to the diameter of molecular hydrogen and allows intercalation of H₂ up to the point where a liquid-like monolayer is formed within the clay. At a low coverage of 0.1 H₂ per cation the isosteric heat of adsorption is 9.2 kJ mol^–1. Quasielastic neutron scattering experiments conducted at 40–100 K reveal two populations of H₂ within the clay. First, we find molecules that are localized close to the partially hydrated Ca²⁺ cations. Second, we identify a more mobile liquid-like population whose motion is captured by jump diffusion. At 40 K, the H₂ diffusion coefficient is 2.3 ± 0.5 × 10^–5 cm² s^–1. This is an order of magnitude slower than the value extrapolated from bulk liquid H₂

Social Work, Modernity and Post modernity

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