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NEXAFS spectroscopy of ionic liquids: experiments versus calculations

Fogarty, Richard M.; Matthews, Richard P.; Clough, Matthew T.; Ashworth, Claire R.; Brandt, Agnieszka; Corbett, Paul J.; Palgrave, Robert G.; Bourne, Richard A.; Chamberlain, Thomas W.; Vander Hoogerstraete, Tom; Thompson, Paul B.J.; Hunt, Patricia A.; Besley, Nicholas A.; Lovelock, Kevin R.J.

Authors

Richard M. Fogarty

Richard P. Matthews

Matthew T. Clough

Claire R. Ashworth

Agnieszka Brandt

Paul J. Corbett

Robert G. Palgrave

Richard A. Bourne

Thomas W. Chamberlain

Tom Vander Hoogerstraete

Paul B.J. Thompson

Patricia A. Hunt

Nicholas A. Besley

Kevin R.J. Lovelock



Abstract

Experimental near edge X–ray absorption fine structure (NEXAFS) spectra are reported for 12 ionic liquids (ILs) encompassing a range of chemical structures for both the sulfur 1s and nitrogen 1s edges and compared with time–dependent density functional theory (TD–DFT) calculations. The energy scales for the experimental data were carefully calibrated against literature data. Gas phase calculations were performed on lone ions, ion pairs and ion pair dimers, with a wide range of ion pair conformers considered. For the first time, it is demonstrated that TD–DFT is a suitable method for simulating NEXAFS spectra of ILs, although the number of ions included in the calculations and their conformations are important considerations. For most of the ILs studied, calculations on lone ions in the gas phase were sufficient to successfully reproduce the experimental NEXAFS spectra. However, for certain ILs – for example, those containing a protic ammonium cation –calculations on ion pairs were required to obtain a good agreement with experimental spectra. Furthermore, significant conformational dependence was observed for the protic ammonium ILs, providing insight into the predominant liquid phase cation–anion interactions. Among the 12 investigated ILs, we find that four have an excited state that is delocalised across both the cation and the anion, which has implications for any process that depends upon the excited state, for example, radiolysis. Considering the collective experimental and theoretical data, we recommend that ion pairs should be the minimum number of ions used for the calculations of NEXAFS spectra of ILs.

Citation

Fogarty, R. M., Matthews, R. P., Clough, M. T., Ashworth, C. R., Brandt, A., Corbett, P. J., …Lovelock, K. R. (in press). NEXAFS spectroscopy of ionic liquids: experiments versus calculations. Physical Chemistry Chemical Physics, https://doi.org/10.1039/C7CP07143D

Journal Article Type Article
Acceptance Date Nov 5, 2017
Online Publication Date Nov 6, 2017
Deposit Date Nov 9, 2017
Publicly Available Date Nov 7, 2018
Journal Physical Chemistry Chemical Physics
Print ISSN 1463-9076
Electronic ISSN 1463-9076
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
DOI https://doi.org/10.1039/C7CP07143D
Public URL https://nottingham-repository.worktribe.com/output/892902
Publisher URL http://pubs.rsc.org/en/content/articlelanding/2017/cp/c7cp07143d#!divAbstract

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