The Hydrated Excess Proton in the Zundel Cation H5O2+: The Role of Ultrafast Solvent Fluctuations
The Hydrated Excess Proton in the Zundel Cation H5O2+: The Role of Ultrafast Solvent Fluctuations
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DOI：
10.1002/anie.201602523
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发表时间：
2016-08-26
影响因子：
16.6
通讯作者：
Elsaesser, Thomas
中科院分区：
文献类型：
--
作者：
Dahms, Fabian;Costard, Rene;Elsaesser, Thomas
经过数十年的广泛研究，液态水中过量质子的性质仍然难以捉摸。鉴于大量水的超快结构波动扰乱了水中过量质子的结构基序，我们在飞秒时间尺度上选择性地探测乙腈中的典型质子化水溶剂化物。我们重点关注在室温乙腈中制备的 Zundel 阳离子 H5O2+，揭示了其振动吸收连续谱的独特特征，并将其与瞬态泵浦探针光谱中的 OH 拉伸和弯曲激发分开。红外吸收连续谱源自 H+ 传递振动及其组合和泛音的强超快频率调制。研究发现 H5O2+ 的振动寿命在 100fs 以下，比非质子化水的振动寿命短得多。理论结果支持了质子水合的图像，其中与溶剂的波动电相互作用和低频模式的随机热激发不断改变质子结合位点，同时影响其运动。
The nature of the excess proton in liquid water has remained elusive after decades of extensive research. In view of ultrafast structural fluctuations of bulk water scrambling the structural motifs of excess protons in water, we selectively probe prototypical protonated water solvates in acetonitrile on the femtosecond time scale. Focusing on the Zundel cation H5O2+ prepared in room-temperature acetonitrile, we unravel the distinct character of its vibrational absorption continuum and separate it from OH stretching and bending excitations in transient pump-probe spectra. The infrared absorption continuum originates from a strong ultrafast frequency modulation of the H+ transfer vibration and its combination and overtones. Vibrational lifetimes of H5O2+ are found to be in the sub-100fs range, much shorter than those of unprotonated water. Theoretical results support a picture of proton hydration where fluctuating electrical interactions with the solvent and stochastic thermal excitations of low-frequency modes continuously modify the proton binding site while affecting its motions.