Picosecond Dynamics of Hydrogen Bond Rearrangements During Phase Separation of a Triethylamine and Water Mixture
Picosecond Dynamics of Hydrogen Bond Rearrangements During Phase Separation of a Triethylamine and Water Mixture
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三乙胺和水混合物相分离过程中氢键重排的皮秒动力学
DOI：
10.1039/c4pp00048j
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发表时间：
2014
影响因子：
3.1
通讯作者：
D. D. Dlott
中科院分区：
文献类型：
--
作者：
S. Kajimoto;N.-H. Seong;H. Fukumura;D. D. Dlott
利用皮秒红外激光脉冲产生的温度跃变和超快拉曼光谱，观察了液态三乙胺（TEA）-水混合物中相分离的最早阶段。水OH伸缩区的拉曼光谱变化表明，由红外脉冲引起的温度上升在几十皮秒内平衡。差拉曼光谱的TEA CH伸缩区的振幅变化由初始较快和随后较慢的过程组成。在100 ps内的更快的过程归因于由温度升高引起的氢键弱化。观察到归因于相分离的较慢过程持续几纳秒，表明TEA和水之间的氢键数量随着时间逐渐减少。相分离过程中氢键断裂的动力学表明相分离的组分的线性增长，如先前在纳秒时间尺度上观察到的，而不是更常见的指数增长。在相分离过程中，在差拉曼光谱中观察到一个峰蓝移。这种转变意味着，涉及非常少的水分子的TEA-水聚集体的氢键断裂发生在相分离的初始阶段（最多2 ns），然后是由水分子包围的TEA-水对的断裂。这种效应可能是由于空间不均匀性与相分离过程：聚集体或集群存在于溶液中，甚至低于较低的临界溶解温度。
The earliest stages of phase separation in a liquid triethylamine (TEA)–water mixture were observed using a picosecond IR laser pulse to produce a temperature jump and ultrafast Raman spectroscopy. Raman spectral changes in the water OH stretching region showed that the temperature rise induced by IR pulses equilibrated within a few tens of picoseconds. Amplitude changes in the TEA CH-stretching region of difference Raman spectra consisted of an initial faster and a subsequent slower process. The faster process within 100 ps is attributed to hydrogen bond weakening caused by the temperature rise. The slower process attributed to phase separation was observed for several nanoseconds, showing the number of hydrogen bond between TEA and water gradually decreased with time. The kinetics of hydrogen bond scission during phase separation indicated a linear growth of the phase-separated component, as observed previously on the nanosecond time scale, rather than the more usual exponential growth. A peak blueshift was observed in the difference Raman spectra during phase separation. This shift implies that hydrogen bond scission of TEA–water aggregates involving very few water molecules took place in the initial stage of phase separation (up to 2 ns), and then was followed by the breaking of TEA–water pairs surrounded by water molecules. This effect may be a result from spatial inhomogeneities associated with the phase separation process: aggregates or clusters existing naturally in solution even below the lower critical soluble temperature.