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Instruments / Technical Area	Publication Details	Published	Actions
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS	Resonant electron spectroscopy: identification of atomic contributions to valence states Jake M. Seymour , Ekaterina Gousseva , Alex Large , Georg Held , Dennis Hein , Garlef Wartner , Wilson Quevedo , Robert Seidel , Claudia Kolbeck , Coby J. Clarke , Richard M. Fogarty , Richard A. Bourne , Roger A. Bennett , Robert G. Palgrave , Patricia A. Hunt , Kevin R. J. Lovelock Faraday Discussions DOI: 10.1039/D1FD00117E Diamond Proposal Number(s): [24304, 25929] Show Abstract ▼ Abstract: Valence electronic structure is crucial for understanding and predicting reactivity. Valence non-resonant X-ray photoelectron spectroscopy (NRXPS) provides a direct method for probing the overall valence electronic structure. However, it is often difficult to separate the varying contributions to NRXPS; for example, contributions of solutes in solvents or functional groups in complex molecules. In this work we show that valence resonant X-ray photoelectron spectroscopy (RXPS) is a vital tool for obtaining atomic contributions to valence states. We combine RXPS with NRXPS and density functional theory calculations to demonstrate the validity of using RXPS to identify atomic contributions for a range of solutes (both neutral and ionic) and solvents (both molecular solvents and ionic liquids). Furthermore, the one-electron picture of RXPS holds for all of the closed shell molecules/ions studied, although the situation for an open-shell metal complex is more complicated. Factors needed to obtain a strong RXPS signal are investigated in order to predict the types of systems RXPS will work best for; a balance of element electronegativity and bonding type is found to be important. Additionally, the dependence of RXPS spectra on both varying solvation environment and varying local-covalent bonding is probed. We find that RXPS is a promising fingerprint method for identifying species in solution, due to the spectral shape having a strong dependence on local-covalency but a weak dependence on solvation environment.	Feb 2022
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS I09-Surface and Interface Structural Analysis	Experimental measurement and prediction of ionic liquid ionisation energies Jake Seymour , Ekaterina Gousseva , Alex Large , Coby J. Clarke , Peter Licence , Richard M. Fogarty , David A. Duncan , Pilar Ferrer , Federica Venturini , Roger A. Bennett , Robert G. Palgrave , Kevin R. J. Lovelock Physical Chemistry Chemical Physics DOI: 10.1039/D1CP02441H Diamond Proposal Number(s): [20463, 24304, 25929] Open Access Show Abstract ▼ Abstract: Ionic liquid (IL) valence electronic structure provides key descriptors for understanding and predicting IL properties. The ionisation energies of 60 ILs are measured and the most readily ionised valence state of each IL (the highest occupied molecular orbital, HOMO) is identified using a combination of X-ray photoelectron spectroscopy (XPS) and synchrotron resonant XPS. A structurally diverse range of cations and anions were studied. The cation gave rise to the HOMO for nine of the 60 ILs presented here, meaning it is energetically more favourable to remove an electron from the cation than the anion. The influence of the cation on the anion electronic structure (and vice versa) were established; the electrostatic effects are well understood and demonstrated to be consistently predictable. We used this knowledge to make predictions of both ionisation energy and HOMO identity for a further 516 ILs, providing a very valuable dataset for benchmarking electronic structure calculations and enabling the development of models linking experimental valence electronic structure descriptors to other IL properties, e.g. electrochemical stability. Furthermore, we provide design rules for the prediction of the electronic structure of ILs.	Sep 2021

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