Liu Liyuan, Bakker Huib J
FOM Institute for Atomic and Molecular Physics, Science Park 104, 1098 XG Amsterdam, The Netherlands.
J Phys Chem B. 2015 Feb 12;119(6):2628-37. doi: 10.1021/jp508862t. Epub 2015 Jan 5.
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.
我们使用飞秒红外瞬态吸收光谱法研究了不同水合水平下Nafion膜中质子水合物的能量弛豫和结构弛豫动力学。在低水合水平下，我们观察到类本征质子水合结构的质子振动激发会导致一个结构弛豫过程，在此过程中类本征结构演变为类祖德尔质子水合结构。这种重组导致质子电荷转移，并紧密遵循由S. Hammes-Schiffer、J. T. Hynes等人提出的红外诱导绝热质子转移机制。在高水合水平下，光谱动力学主要由振动能量弛豫以及随后质子水合结构和周围水分子的冷却主导。通过对瞬态光谱数据进行动力学分析，我们确定了质子转移、振动能量弛豫和冷却速率随水合水平的变化关系。我们发现，红外诱导的质子转移在所有水合水平下都会发生，但在高水合水平下由于振动能量弛豫的影响日益占主导地位，因而变得不太明显。
