Vibrational Excitation Induced Proton Transfer in Hydrated Nafion Membranes
Vibrational Excitation Induced Proton Transfer in Hydrated Nafion Membranes
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DOI：
10.1021/jp508862t
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发表时间：
2015-02-12
影响因子：
3.3
通讯作者：
Bakker, Huib J.
中科院分区：
文献类型：
--
作者：
Liu, Liyuan;Bakker, Huib J.
利用飞秒红外瞬时吸收光谱研究了不同水化程度的Nafion膜中水合质子的能量驰豫和结构驰豫动力学。在低水化水平下，我们观察到类本征质子水化结构的质子振动激发导致了一个结构松弛过程，在此过程中类本征质子水化结构演化为类Zundel质子水化结构。这种重组导致了质子电荷的转移，并与S.Hammes-Schiffer，J.T.Hynes等人提出的红外诱导绝热质子转移的机制密切相关。在高水合水平下，质子水合结构和周围水分子的振动能弛豫和随后的冷却主导了光谱动力学。通过对瞬变光谱数据的动力学分析，我们确定了质子转移速率、振动能弛豫速率和冷却速率作为水合水平的函数。我们发现，红外诱导的质子转移发生在所有水化水平，但在高水化水平变得不那么明显，这是因为振动能弛豫的影响越来越明显。
We study the energy relaxation and structural relaxation dynamics of hydrated protons in Nafion membranes at different hydration levels using femtosecond infrared transient absorption spectroscopy. At low hydration levels we observe that the excitation of the proton vibration of an Eigen-like proton hydration structure leads to a structural relaxation process in which the Eigen-like structure evolves to a Zundel-like proton hydration structure. This reorganization leads to a transfer of the proton charge and closely follows the mechanism of infrared-induced adiabatic proton transfer that has been proposed by S. Hammes-Schiffer, J. T. Hynes, and others. At high hydration levels, the spectral dynamics are dominated by vibrational energy relaxation and subsequent cooling of the proton hydration structures and the surrounding water molecules. Using a kinetic analysis of the transient spectral data, we determine the rates of proton transfer, vibrational energy relaxation, and cooling as a function of hydration level. We find that infrared-induced proton transfer occurs at all hydration levels but becomes less observable at high hydration levels due to the increasingly dominant influence of the vibrational energy relaxation.