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Kinetic isotope effects on hydrogen/deuterium disordering and ordering in ice crystals: A Raman and dielectric study of ice VI, XV, and XIX.
- Source :
-
The Journal of chemical physics [J Chem Phys] 2024 Jun 28; Vol. 160 (24). - Publication Year :
- 2024
-
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.<br /> (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).)
Details
- Language :
- English
- ISSN :
- 1089-7690
- Volume :
- 160
- Issue :
- 24
- Database :
- MEDLINE
- Journal :
- The Journal of chemical physics
- Publication Type :
- Academic Journal
- Accession number :
- 38934633
- Full Text :
- https://doi.org/10.1063/5.0211427