Collective proton transfer in ordinary ice: local environments, temperature dependence and deuteration effects.
Collective proton transfer in ordinary ice: local environments, temperature dependence and deuteration effects.
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DOI：
10.1039/c6cp05679b
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发表时间：
2017-01
期刊：
影响因子：
--
通讯作者：
C. Drechsel-Grau;D. Marx
中科院分区：
文献类型：
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作者：
C. Drechsel-Grau;D. Marx
氢键网络中多个质子的转移通常一次发生一个质子。在足够高的温度下，每个质子通过热激活跳跃沿着其氢键转移，从而使电荷缺陷移动通过网络。在低温下，量子力学隧穿可能会发生，从而避免越过能量势垒。在几个转移质子的情况下，由于电荷缺陷的显著产生，单个质子的独立热跳跃或量子隧穿变得不太有利。例如，在单个分子或氢键分子复合物中，经常发现双质子转移是协同的。避免电荷缺陷的多质子转移可以发生在由几个氢键构建的环状拓扑结构中，所述氢键允许质子转移的定向链。这需要在这些环内完美的质子秩序，这强加了手性和手性，并在所有质子转移时改变宇称。普通冰，也就是六边形冰Ih，是在环境压力下冷冻液态水获得的最稳定的结晶冰形式，由相互连接的六个氧原子环组成，每个氧原子环上有六个质子。这些六边形环即使在低温下也保持质子无序，这是由冰的剩余熵Ih所预示的。然而，由于组合学，这六个环中的一定数量在宏观晶体中是质子有序的。这些手性六聚环可能支持宿主质子的相干隧穿。事实上，在最近的文献中，有一些证据，无论是实验还是模拟，都表明如果温度足够低，在冰Ih中的质子有序六环中，所有六个质子的相关隧穿可能是可能的。在这个角度来看，关键的想法和以前的研究结果将进行审查，根据相关的实验，重点放在可用的从头算路径积分模拟工作补充本文提供的额外数据。
The transfer of multiple protons in hydrogen-bonded networks usually occurs one proton at a time. At sufficiently high temperatures, each proton transfers via thermally activated hopping along its hydrogen bond, thereby moving a charge defect through the network. At low temperatures, quantum-mechanical tunnelling might set in instead, thus avoiding hopping over the energy barriers. In the case of several transferring protons, independent thermal hopping or quantum tunnelling of the individual protons becomes less favourable because of a significant creation of charge defects. In individual molecules or hydrogen-bonded molecular complexes, for instance, double proton transfer is often found to be concerted. Multiple proton transfer that avoids charge defects can occur in cyclic topologies built from several hydrogen bonds that allow for directional chains of proton transfer. This requires perfect proton order within these rings, which imposes handedness and thus chirality, and changes parity upon transfer of all protons. Ordinary ice, which is hexagonal ice Ih, is the most stable form of crystalline ice obtained upon freezing liquid water at ambient pressure and consists of interconnected six rings of oxygen atoms that host six protons each. These hexagonal rings remain proton disordered even down to low temperatures, as heralded by the residual entropy of ice Ih. However, owing to combinatorics, a certain number of these six rings is proton ordered in macroscopic crystals. These chiral hexameric rings might support coherent tunnelling of the hosted protons. Indeed, there is some evidence in the recent literature, both experimental and simulational, that correlated tunnelling of all six protons might be possible in proton-ordered six rings in ice Ih if temperatures are low enough. In this Perspective, the key ideas and previous findings will be reviewed in the light of relevant experiments with a focus on available ab initio path integral simulation work supplemented with additional data provided herein.