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Immobility of protons in ice from 30 to 190 K

机译：质子在冰中的固定性从30到190 K

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The anomalously fast motion of hydronium ions (H_3O~+) in water is often attributed to the Grotthuss mechanism, whereby protons tunnel from one water molecule to the next. This tunnelling is relevant to proton motion through water in restricted geometries, such as in 'proton wires' in proteins and in stratospheric ice particles. Transport of hydronium ions in ice is thought to be closely related to its transport in water. But whereas claims have been made that such tunnelling can persist even at 0 K in ice, counter-claims suggest that the activation energy for hydronium motion in ice is non-zero. Here we use 'soft-landing' of hydronium ions on the surface of ice to show that the ions do not seem to move at all at temperatures below 190 K. This implies not only that hydronium motion is an activated process, but also that it does not occur at anything like the rate expected from the Grotthuss mechanism. We also observe the motion of an important kind of defect in ice's hydrogen-bonded structure (the D defect). Extrapolation of our measurements to 0 K indicates that the defect is still mobile at this temperature, in an electric field of 1.6 x 10~8Vm~(-1).
机译：水中氢离子（H_3O〜+）异常快速的运动通常归因于格罗特斯（Grotthuss）机理，质子由此从一个水分子隧穿到另一个水分子。这种隧穿与质子在有限的几何形状中穿过水的质子运动有关，例如在蛋白质和平流层冰粒中的“质子丝”中。人们认为，氢离子在冰中的运输与其在水中的运输密切相关。但是，尽管有人声称这种隧穿即使在冰上甚至在0 K时也可以持续，但反诉却表明，在冰中水合氢分子运动的活化能非零。在这里，我们使用水合氢离子在冰表面的“软着陆”来显示离子在190 K以下的温度下似乎根本不会移动。这不仅意味着水合氢运动是一个激活的过程，而且还暗示不会像格罗特斯机制所预期的那样发生。我们还观察到冰的氢键结构中一种重要缺陷（D缺陷）的运动。我们的测量值外推到0 K，表明该缺陷在1.6 x 10〜8Vm〜（-1）的电场下仍可移动。

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