Mamontov E
National Institute of Standards and Technology (NIST) Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8562, USA.
J Chem Phys. 2005 Jul 8;123(2):24706. doi: 10.1063/1.1949171.
We have performed a quasielastic neutron-scattering experiment on backscattering spectrometer with sub-mueV resolution to investigate the slow dynamics of surface water in zirconium oxide using the sample studied previously with a time-of-flight neutron spectrometer [E. Mamontov, J. Chem. Phys. 121, 9087 (2004)]. The backscattering measurements in the temperature range of 240-300 K have revealed a translational dynamics slower by another order of magnitude compared to the translational dynamics of the outer hydration layer observed in the time-of-flight experiment. The relaxation function of this slow motion is described by a stretched exponential with the stretch factors between 0.8 and 0.9, indicating a distribution of the relaxation times. The temperature dependence of the average residence time is non-Arrhenius, suggesting that the translational motion studied in this work is more complex than surface jump diffusion previously observed for the molecules of the outer hydration layer. The observed slow dynamics is ascribed to the molecules of the inner hydration layer that form more hydrogen bonds compared to the molecules of the outer hydration layer. Despite being slower by two orders of magnitude, the translational motion of the molecules of the inner hydration layer may have more in common with bulk water compared to the outer hydration layer, the dynamics of which is slower than that of bulk water by just one order of magnitude.
我们使用先前通过飞行时间中子光谱仪研究过的样品[E. 马蒙托夫，《化学物理杂志》121, 9087 (2004)]，在具有亚微电子伏特分辨率的背散射光谱仪上进行了准弹性中子散射实验，以研究氧化锆表面水的慢动力学。在240 - 300 K温度范围内的背散射测量结果表明，与飞行时间实验中观察到的外部水合层的平移动力学相比，其平移动力学要慢一个数量级。这种慢运动的弛豫函数由拉伸指数描述，拉伸因子在0.8到0.9之间，这表明弛豫时间存在分布。平均停留时间的温度依赖性是非阿仑尼乌斯型的，这表明这项工作中研究的平动运动比先前在外部水合层分子中观察到的表面跳跃扩散更为复杂。观察到的慢动力学归因于内部水合层的分子，与外部水合层的分子相比，它们形成了更多的氢键。尽管内部水合层分子的平动运动比外部水合层慢两个数量级，但与外部水合层相比，其与本体水可能有更多的共同之处，外部水合层的动力学仅比本体水慢一个数量级。
