FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
J Chem Phys. 2011 Sep 28;135(12):124517. doi: 10.1063/1.3643763.
We report the vibrational and orientational dynamics of water molecules in isotopically diluted NaOH and NaOD solutions using polarization-resolved femtosecond vibrational spectroscopy and terahertz time-domain dielectric relaxation measurements. We observe a speed-up of the vibrational relaxation of the O-D stretching vibration of HDO molecules outside the first hydration shell of OH(-) from 1.7 ± 0.2 ps for neat water to 1.0 ± 0.2 ps for a solution of 5 M NaOH in HDO:H(2)O. For the O-H vibration of HDO molecules outside the first hydration shell of OD(-), we observe a similar speed-up from 750 ± 50 fs to 600 ± 50 fs for a solution of 6 M NaOD in HDO:D(2)O. The acceleration of the decay is assigned to fluctuations in the energy levels of the HDO molecules due to charge transfer events and charge fluctuations. The reorientation dynamics of water molecules outside the first hydration shell are observed to show the same time constant of 2.5 ± 0.2 ps as in bulk liquid water, indicating that there is no long range effect of the hydroxide ion on the hydrogen-bond structure of liquid water. The terahertz dielectric relaxation experiments show that the transfer of the hydroxide ion through liquid water involves the simultaneous motion of ~7 surrounding water molecules, considerably less than previously reported for the proton.
我们使用偏振分辨飞秒振动光谱和太赫兹时域介电弛豫测量研究了在同位素稀释的 NaOH 和 NaOD 溶液中水分子的振动和取向动力学。我们观察到 HDO 分子的 O-D 伸缩振动在 OH(-)的第一水合壳外的振动弛豫速度加快，从纯水中的 1.7±0.2 ps 加快到 5 M NaOH 在 HDO:H2O 溶液中的 1.0±0.2 ps。对于 OD(-)的第一水合壳外的 HDO 分子的 O-H 振动，我们观察到类似的加速，从 6 M NaOD 在 HDO:D2O 溶液中的 750±50 fs 加快到 600±50 fs。这种衰减的加速归因于 HDO 分子能级的波动，这是由于电荷转移事件和电荷波动引起的。我们观察到第一水合壳外的水分子的重新取向动力学表现出与在液态水中相同的 2.5±0.2 ps 的时间常数，这表明氢氧根离子对液态水的氢键结构没有远程影响。太赫兹介电弛豫实验表明，氢氧根离子通过液态水的传递涉及到~7 个周围水分子的同时运动，这比以前报道的质子的运动要少得多。
