Accumulating evidence for the Zundel motif In recent years, vibrational spectroscopy has been homing in on how water accommodates dissolved protons in acidic solution. Most such studies have examined adjacent stretching or bending modes. Dahms et al. pinpoint the vibrational dynamics of the acidic proton itself, which is sandwiched between two water molecules in a so-called Zundel motif. Comparing spectra in bulk water and in acetonitrile (a known Zundel host) revealed the persistence of this motif in aqueous acid on a subpicosecond time scale. Persistence is sustained by the hydrogen-bonding network among the surrounding water molecules. Science, this issue p. 491 Comparison of vibrational dynamics in acidified water and acidified acetonitrile supports the prevalence of the Zundel motif. Solvation and transport of excess protons in aqueous systems play a fundamental role in acid-base chemistry and biochemical processes. We mapped ultrafast proton excursions along the proton transfer coordinate by means of two-dimensional infrared spectroscopy, both in bulk water and in a Zundel cation (H5O2)+ motif selectively prepared in acetonitrile. Electric fields from the environment and stochastic hydrogen bond motions induce fluctuations of the proton double-minimum potential. Within the lifetime of a particular hydration geometry, the proton explores a multitude of positions on a sub-100-femtosecond time scale. The proton transfer vibration is strongly damped by its 20- to 40-femtosecond population decay. Our results suggest a central role of Zundel-like geometries in aqueous proton solvation and transport.

中文翻译：

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超快二维红外光谱绘制的水合过剩质子的大振幅转移运动

为 Zundel 基序积累证据 近年来，振动光谱学一直致力于研究水如何容纳酸性溶液中的溶解质子。大多数此类研究都检查了相邻的拉伸或弯曲模式。达姆斯等人。精确定位酸性质子本身的振动动力学，它夹在两个水分子之间，形成所谓的 Zundel 基序。比较散装水和乙腈（一种已知的 Zundel 宿主）中的光谱，揭示了该基序在亚皮秒时间尺度上在含水酸中的持久性。持久性是由周围水分子之间的氢键网络维持的。科学，这个问题 p。491 酸化水和酸化乙腈中振动动力学的比较支持 Zundel 基序的流行。水性体系中过量质子的溶解和传输在酸碱化学和生化过程中起着重要作用。我们通过二维红外光谱法绘制了沿质子转移坐标的超快质子偏移，无论是在散装水中还是在乙腈中选择性制备的 Zundel 阳离子 (H5O2)+ 基序中。来自环境的电场和随机氢键运动会引起质子双极小电势的波动。在特定水合几何形状的生命周期内，质子在亚 100 飞秒的时间尺度上探索多个位置。质子转移振动被其 20 到 40 飞秒的种群衰减强烈抑制。我们的结果表明类似 Zundel 的几何形状在水性质子溶剂化和传输中起着核心作用。