Miskowiec Andrew, Niedziela J L, Kirkegaard Marie C, Shields Ashley E
Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
University of Tennessee, Knoxville, TN, 37996, USA.
Sci Rep. 2019 Jul 19;9(1):10476. doi: 10.1038/s41598-019-46675-x.
Inelastic neutron scattering (INS) is uniquely sensitive to hydrogen due to its comparatively large thermal neutron scattering cross-section (82 b). Consequently, the inclusion of water in real samples presents significant challenges to INS data analysis due directly to the scattering strength of hydrogen. Here, we investigate uranyl fluoride (UOF) with inelastic neutron scattering. UOF is the hydrolysis product of uranium hexafluoride (UF), and is a hygroscopic, uranyl-ion containing particulate. Raman spectral signatures are commonly used for inferential understanding of the chemical environment for the uranyl ion in UOF, but no direct measurement of the influence of absorbed water molecules on the overall lattice dynamics has been performed until now. To deconvolute the influence of waters on the observed INS spectra, we use density functional theory with full spectral modeling to separate lattice motion from water coupling. In particular, we present a careful and novel analysis of the Q-dependent Debye-Waller factor, allowing us to separate spectral contributions by mass, which reveals preferential water coupling to the uranyl stretching vibrations. Coupled with the detailed partial phonon densities of states calculated via DFT, we infer the probable adsorption locations of interlayer waters. We explain that a common spectral feature in Raman spectra of uranyl fluoride originates from the interaction of water molecules with the uranyl ion based on this analysis. The Debye-Waller analysis is applicable to all INS spectra and could be used to identify light element contributions in other systems.
非弹性中子散射（INS）对氢具有独特的敏感性，这是因为氢具有相对较大的热中子散射截面（82靶恩）。因此，由于氢的散射强度，实际样品中含有水给INS数据分析带来了重大挑战。在这里，我们用非弹性中子散射研究了氟化铀酰（UOF）。UOF是六氟化铀（UF）的水解产物，是一种含有铀酰离子的吸湿性颗粒。拉曼光谱特征通常用于推断UOF中铀酰离子的化学环境，但到目前为止，尚未对吸收的水分子对整体晶格动力学的影响进行直接测量。为了反卷积水对观测到的INS光谱的影响，我们使用密度泛函理论和全光谱建模来分离晶格运动和水的耦合。特别是，我们对与Q相关的德拜-瓦勒因子进行了细致而新颖的分析，使我们能够按质量分离光谱贡献，这揭示了水与铀酰伸缩振动的优先耦合。结合通过密度泛函理论计算的详细部分声子态密度，我们推断了层间水的可能吸附位置。基于此分析，我们解释了氟化铀酰拉曼光谱中一个常见的光谱特征源于水分子与铀酰离子的相互作用。德拜-瓦勒分析适用于所有INS光谱，可用于识别其他系统中的轻元素贡献。
