Identification of Transient Radical Anions (LiClO4)n– (n = 1–3) in THF Solutions: Experimental and Theoretical Investigation on Electron Localization in Oligomers

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• 作者：Jun Ma ; Pierre Archirel ; Pascal Pernot ; Uli Schmidhammer ; Sophie Le Ca?r ; Mehran Mostafavi
• 刊名：Journal of Physical Chemistry B
• 出版年：2016
• 出版时间：February 4, 2016
• 年：2016
• 卷：120
• 期：4
• 页码：773-784
• 全文大小：772K
• ISSN：1520-5207

文摘

Picosecond pulse radiolysis measurements of tetrahydrofuran (THF) solutions containing LiClO₄ over a wide range of concentration are performed to investigate the formation of transient species. The ³⁵Cl NMR measurements of these solutions prior to irradiation show that the salt is in the form of (LiClO₄)_n oligomers. Kinetics and transient absorption spectra of intermediates in each solution are obtained on the time scale from 10 to 3800 ps. A global spectro-kinetic matrix of the data is analyzed by the multicurve resolution alternated least-squares (MCR-ALS) method. It shows the presence of 3 transient species induced by electron pulse, in addition to the solvated electron. A hybrid Monte Carlo/DFT molecular simulation method is elaborated, using the MPW1K functional for the configuration sampling and B3LYP for the spectra calculations. The maximum of the absorption band of the monomer (LiClO₄)^?, dimer (LiClO₄)₂^–, trimer (LiClO₄)₃^–, and tetramer (LiClO₄)₄^– anions are deduced from the simulations. They enable one to label the MCR-ALS spectra (differences are below 0.1 eV) and to interpret the kinetic data. The simulations show also that Li^I ion catalyzes the reduction of perchlorate by excess electrons. Only the dimer anion, due to its unique structure with a stable Li₂⁺ core and two nonbridging perchlorates, presents higher stability toward ClO₄^– reduction into ClO₃^–. It corresponds to the long-lived species observed in the experiments.