We confirm that synthetic uranyl hydroxide hydrate metaschoepite [(UO)2₄O(OH)₆]·5H₂O is unstable against dehydration under dry conditions, and we present a structural and vibrational spectroscopic study of synthetic metaschoepite and its ambient temperature dehydration product. Complementary structural (X-ray diffraction and neutron diffraction) and vibrational spectroscopic techniques (Raman spectroscopy, infrared spectroscopy, and inelastic neutron scattering) are used to probe different components of these species. Analysis of the dehydration product suggests that it contains both pentagonally coordinated and hexagonally coordinated uranyl ions, necessitating that some uranyl ions undergo a coordination change during the dehydration of pentagonally coordinated metaschoepite. Vibrational spectra of metaschoepite and its dehydration product are interpreted with power spectra generated from ab initio molecular dynamics trajectories, allowing assignment of all major features. We identify the uranyl symmetric stretching modes of the four distinct uranyl ions in synthetic metaschoepite and clarify the assignment of lower energy Raman modes in both structures. The coanalysis of experimental and computational data reveals a strong coupling between the uranyl stretching modes and hydroxide bending modes in the anhydrous structure, leading to the presence of several high-energy combination bands in the inelastic neutron scattering data.

中文翻译：

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合成次锂铁矿及其脱水产物的结构和振动光谱的阐明

我们确认合成的铀酰氢氧化物水合变锰矿[（UO）2 ₄ O（OH）₆ ]·5H ₂O在干燥条件下对脱水不稳定，我们提供了合成变金属锂及其室温脱水产物的结构和振动光谱研究。互补结构（X射线衍射和中子衍射）和振动光谱技术（拉曼光谱，红外光谱和非弹性中子散射）用于探测这些物质的不同成分。脱水产物的分析表明，它同时含有五角配位和六边形配位的铀酰离子，因此在五角配位变硬沸石的脱水过程中，某些铀酰离子必须经历配位变化。通过从头算的分子动力学轨迹生成的功率谱，可以解释变菱镁矿及其脱水产物的振动光谱，从而可以分配所有主要特征。我们确定了合成次生辉石中四个不同的铀酰离子的铀酰对称拉伸模式，并阐明了两种结构中低能拉曼模式的分配。实验和计算数据的共同分析揭示了无水结构中铀酰拉伸模式和氢氧化物弯曲模式之间的强耦合，导致在非弹性中子散射数据中存在多个高能组合谱带。我们确定了合成次生辉石中四个不同的铀酰离子的铀酰对称拉伸模式，并阐明了两种结构中低能拉曼模式的分配。实验和计算数据的共同分析揭示了无水结构中铀酰拉伸模式和氢氧化物弯曲模式之间的强耦合，导致在非弹性中子散射数据中存在多个高能组合谱带。我们确定了合成次生辉石中四个不同的铀酰离子的铀酰对称拉伸模式，并阐明了两种结构中低能拉曼模式的分配。实验和计算数据的共同分析揭示了无水结构中铀酰拉伸模式和氢氧化物弯曲模式之间的强耦合，导致在非弹性中子散射数据中存在多个高能组合谱带。