Impact of Film Thickness and Temperature on Ultrafast Excess Charge Dynamics in Ionic Liquid Films

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• 作者：Alex J. Shearer ; David E. Suich ; Benjamin W. Caplins ; Charles B. Harris
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：October 29, 2015
• 年：2015
• 卷：119
• 期：43
• 页码：24417-24424
• 全文大小：427K
• ISSN：1932-7455

文摘

Ultrafast response of the room temperature ionic liquid (RTIL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Bmpyr][NTfb>2b>]) to a photoinjected electron is investigated in few-monolayer films using time- and angle-resolved two-photon photoemission spectroscopy. A delocalized precursor state and a localized solvated state were resolved at early times, but after 200 fs only a single solvated state was observed. The dynamics of film response to this solvated state were shown to depend significantly on film temperature and thickness. Population lifetime measurements demonstrated that the RTIL film can significantly affect the coupling between solvated state and metal substrate, as the solvated state鈥檚 average lifetime increased from 90 卤 20 fs in 1 ML films to 195 卤 83 ps in 3 ML films. Additionally, a temperature dependence of the time-dependent binding energy shift of the solvated state after ca. 500 fs was attributed to a phase change occurring between the two temperature regimes that were investigated. Results from xenon overlayer experiments suggest that the solvation process occurs near the surface of the RTIL film. Finally, film degradation was found to be present, suggesting that the observed solvation response could involve a radical species.