Quantifying Actinide-Ligand Covalency with Resonant Inelastic X-ray Scattering

用共振非弹性 X 射线散射量化锕系配体共价

• 批准号: EP/V029347/1
• 负责人: Michael Lloyd Baker
• 金额: $ 51.31万
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FV029347%2F1
• 关键词: Quantifying; Actinide; Ligand; Covalency; Resonant

The UK has invested in world-leading synchrotron X-ray facilities. This includes state-of-the-art resonant inelastic X-ray scattering (RIXS) techniques that measure electronic structure with unprecedented energy resolution. RIXS is, however, infrequently applied to its full potential due to a lack of analytical expertise that limits quantitative insights. The least developed area of all is the analysis of actinide RIXS. Actinides are amongst the largest elements within the periodic table, and their chemistry is notoriously challenging to predict. The development of RIXS at energies suitable for accessing actinides has opened up an unexplored avenue to experimentally measure actinide physical and chemical properties. RIXS is an element-specific technique that targets the outer actinide orbitals. The method is therefore selectively sensitive to how actinide orbitals engage in bonding at the molecular level. This project aims to develop RIXS into a quantitative tool to advance understanding of how actinides engage in chemical bonding. The extent and nature of bond-covalency is of particular importance since this profoundly influences physical properties, reactivity and the selectivity of actinide bond formation. There is much debate concerning the covalency of actinide bonding. On one hand, covalency can be considered as the mixing of electron density between atoms, and on the other covalency can be understood as occurring when the energy of the actinide and bonding atom orbitals match up. There are few experimental techniques with sensitivity to actinide covalency, and those that exist are limited to specific cases, i.e. only certain oxidation states, or types of bonded atom. RIXS has the potential to bridge the gap between the synthetic isolation of actinide compounds and first principle theory. Preliminary research by the PI has confirmed the sensitivity of RIXS to uranium bond covalency, identifying opportunities to advance understanding of actinide bonding.The complex chemical bonding properties of actinides represent a major challenge to the nuclear energy sector. This project will develop methodologies and new knowledge that could lead to improved processes for the separation of actinides from other elements in nuclear waste processing and to better understand how actinides interact within the environment. The proposed research requires an equal combination of RIXS measurement and theoretical simulations. Multiple levels of theory will be applied to identify the most accurate means to simulate spectra. Advances in synthetic chemistry have provided systematic families of compounds, that will be used to identify spectral trends, aiding the development of RIXS analysis. The focus will be on uranium and thorium, but the methods developed will be equally relevant to the study of transuranic compounds. The RIXS measurement methodologies, analysis and simulation methods developed will be distributed in an easy to use software package, to put the full potential of RIXS into the hands of the X-ray community.Initial studies will explore donor covalency in single and double bonds to elucidate how RIXS spectral shape correlates with electronic structure. Less explored situations will be investigated, including compounds predicted as being highly covalent.The developed RIXS analysis methods will then be applied to novel molecules prepared by collaborators and project partners. This will include a series of molecules that can adopt a variety of metal ions down a full column of the periodic table, such that our newfound understanding of U and Th bonding can be placed within the larger context of the periodic table. Finally, the complementary use of L and M-edge RIXS will be applied to pin down one of the most controversial and elusive problems in actinide electronic structure: the varying extent of 5f versus 6d orbital contributions to covalency.

英国已经投资了世界领先的同步辐射X射线设备。这包括最先进的共振非弹性X射线散射(RIXS)技术，该技术以前所未有的能量分辨率测量电子结构。然而，由于缺乏限制定量洞察的分析专业知识，RIXS很少被应用于其全部潜力。最不发达的领域就是榄系元素RIXS的分析。吖系元素是元素周期表中最大的元素之一，它们的化学成分是出了名的难以预测。RIXS的发展，在适合于访问鳗系元素的能量下，开辟了一条未知的途径，用于实验测量鳗系元素的物理和化学性质。RIXS是一种特定于元素的技术，其目标是外层鳗系元素的轨道。因此，该方法对榄系元素轨道如何在分子水平上参与成键具有选择性的敏感性。该项目旨在将RIXS发展成为一种定量工具，以促进对吖系元素如何参与化学键的理解。键-共价性的程度和性质特别重要，因为它深刻地影响物理性质、反应性和榄系元素键形成的选择性。关于鳗系元素键的共价性有很大的争论。一方面，共价性可以被认为是原子之间电子密度的混合，另一方面，共价性可以被理解为当榄系元素和成键原子轨道的能量匹配时发生的共价性。很少有实验技术对鳗系元素的共价性敏感，存在的技术仅限于特定情况，即只有某些氧化态或键合原子的类型。RIXS有可能在鳗系化合物的合成分离和第一性原理理论之间架起一座桥梁。PI的初步研究证实了RIXS对铀键共价性的敏感性，确定了增进对鳗系元素成键的理解的机会。该项目将发展方法论和新知识，以改进在核废料处理过程中将放线元素与其他元素分离的过程，并更好地了解放线元素在环境中如何相互作用。拟议的研究需要RIXS测量和理论模拟的平等结合。将应用多层次的理论来确定最准确的光谱模拟方法。合成化学的进步提供了系统的化合物家族，这些化合物将用于确定光谱趋势，有助于RIXS分析的发展。重点将放在铀和钍上，但开发的方法将同样与超铀化合物的研究相关。开发的RIXS测量方法、分析和模拟方法将发布在一个易于使用的软件包中，以便将RIXS的全部潜力交给X射线工作者。初步研究将探索单键和双键中的施主共价性，以阐明RIXS光谱形状与电子结构的关系。较少探索的情况将被调查，包括预测为高共价的化合物。然后，开发的RIXS分析方法将应用于由合作者和项目合作伙伴制备的新型分子。这将包括一系列分子，它们可以沿着元素周期表的一整列采用各种金属离子，这样我们对U和Th键的新理解就可以放在元素周期表的更大背景下。最后，L和M-EDGE RIXS的互补使用将被用来解决鳗系元素电子结构中最有争议和最难以捉摸的问题之一：5f和6d轨道对共价性贡献的不同程度。

项目成果

Sulfidation and Reoxidation of U(VI)-Incorporated Goethite: Implications for U Retention during Sub-Surface Redox Cycling.

• DOI: 10.1021/acs.est.2c05314
• 发表时间: 2022-12-20
• 期刊: ENVIRONMENTAL SCIENCE & TECHNOLOGY
• 影响因子: 11.4
• 作者: Stagg, Olwen;Morris, Katherine;Townsend, Luke Thomas;Kvashnina, Kristina O.;Baker, Michael L.;Dempsey, Ryan L.;Abrahamsen-Mills, Liam;Shaw, Samuel
• 通讯作者: Shaw, Samuel