Femtosecond mid-infrared study of the reorientation of weakly hydrogen-bonded water molecules.
Femtosecond mid-infrared study of the reorientation of weakly hydrogen-bonded water molecules.
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DOI：
10.1021/jp501240e
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发表时间：
2014-05
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影响因子：
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通讯作者：
S. T. van der Post;H. Bakker
中科院分区：
文献类型：
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作者：
S. T. van der Post;H. Bakker
利用偏振分辨双色飞秒中红外光谱研究了弱氢键水分子的光谱扩散和各向异性动力学，研究了弱氢键水分子的氢键和重定向动力学。我们通过将一个相对窄带的激发脉冲调谐到H2O水中HDO分子O-D拉伸振动的高频翼，选择性地激发弱氢键水分子。我们观察到光谱扩散和各向异性都表现出明显的双指数动力学。在前人工作的基础上，将时间常数为~ 100 fs的光谱动力学快速分量分配给快速氢键转换事件。我们观察到这些开关事件对激发的O-D基团的各向异性有明显的影响，这表明光谱弛豫伴随着O-D基团取向的大变化。谱弛豫的慢分量可以归结为液态水氢键网络的集体结构重组。随着温度的升高，光谱弛豫表现出与平均分子重定向相似的加速度，表明这两个过程密切相关。
We study the hydrogen-bond and reorientation dynamics of weakly hydrogen-bonded water molecules by studying their spectral diffusion and anisotropy dynamics with polarization-resolved two-color femtosecond mid-infrared spectroscopy. We selectively excite weakly hydrogen-bonded water molecules by tuning a relatively narrow band excitation pulse far into the high-frequency wing of the O-D stretch vibration of HDO molecules in H2O water. We observe that the spectral diffusion and the anisotropy both show pronounced biexponential dynamics. On the basis of previous work, the fast component of the spectral dynamics with a time constant of ∼100 fs is assigned to rapid hydrogen-bond switching events. We observed that these switching events lead to a pronounced effect on the anisotropy of the excited O-D groups, which shows that the spectral relaxation is accompanied by a large change of the orientation of the O-D groups. The slow component of the spectral relaxation can be assigned to the collective structural reorganization of the hydrogen-bond network of liquid water. With increasing temperature, the spectral relaxation shows a similar acceleration as the average molecular reorientation, showing that these processes are intimately connected.