Alexander V Thoeny, Tobias M Gasser, Lars Hoffmann, Markus Keppler, Roland Böhmer, Thomas Loerting
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引用次数: 0
Abstract
Ice XIX and ice XV are both partly hydrogen-ordered counterparts to disordered ice VI. The ice XIX → XV transition represents the only order-to-order transition in ice physics. Using Raman and dielectric spectroscopies, we investigate the ambient-pressure kinetics of the two individual steps in this transition in real time (of hours), that is, ice XIX → transient ice VI (the latter called VI‡) and ice VI‡ → ice XV. Hydrogen-disordered ice VI‡ appears intermittent between 101 and 120 K, as inferred from the appearance and subsequent disappearance of the ice VI Raman marker bands. A comparison of the rate constants for the H2O ices reported here with those from D2O samples [Thoeny et al., J. Chem. Phys. 156, 154507 (2022)] reveals a large kinetic isotope effect for the ice XIX decay, but a much smaller one for the ice XV buildup. An enhancement of the classical overbarrier rate through quantum tunneling for the former can provide a possible explanation for this finding. The activation barriers for both transitions are in the 18-24 kJ/mol range, which corresponds to the energy required to break a single hydrogen bond. These barriers do not show an H/D isotope effect and are the same, no matter whether they are derived from Raman scattering or from dielectric spectroscopy. These findings favor the notion that a dipolar reorientation, involving the breakage of a hydrogen bond, is the rate determining step at the order-to-order transition.
冰 XIX 和冰 XV 都是无序冰 VI 的部分氢有序对应物。冰 XIX → 冰 XV 的转变代表了冰物理学中唯一的有序到无序转变。利用拉曼光谱和介电光谱,我们研究了这一转变过程中两个单独步骤的实时(小时)环境压力动力学,即冰 XIX → 瞬态冰 VI(后者称为 VI‡)和冰 VI‡ → 冰 XV。从冰 VI 拉曼标记带的出现和随后的消失可以推断,氢有序冰 VI‡ 在 101 至 120 K 之间是间歇性的。将此处报告的 H2O 冰的速率常数与 D2O 样品的速率常数[Thoeny 等人,J. Chem. Phys. 156, 154507 (2022)]进行比较后发现,冰 XIX 的衰变具有很大的动力学同位素效应,而冰 XV 的堆积则小得多。前者通过量子隧穿提高了经典过垒率,这可以解释这一发现。这两种转变的活化势垒都在 18-24 kJ/mol 的范围内,相当于断裂一个氢键所需的能量。无论从拉曼散射法还是介电光谱法得出的结果都是一样的。这些发现支持这样一种观点,即涉及氢键断裂的双极重新定向是有序到无序转变的决定性步骤。
期刊介绍:
The Journal of Chemical Physics publishes quantitative and rigorous science of long-lasting value in methods and applications of chemical physics. The Journal also publishes brief Communications of significant new findings, Perspectives on the latest advances in the field, and Special Topic issues. The Journal focuses on innovative research in experimental and theoretical areas of chemical physics, including spectroscopy, dynamics, kinetics, statistical mechanics, and quantum mechanics. In addition, topical areas such as polymers, soft matter, materials, surfaces/interfaces, and systems of biological relevance are of increasing importance.
Topical coverage includes:
Theoretical Methods and Algorithms
Advanced Experimental Techniques
Atoms, Molecules, and Clusters
Liquids, Glasses, and Crystals
Surfaces, Interfaces, and Materials
Polymers and Soft Matter
Biological Molecules and Networks.