Reorientation Dynamics of Nanoconfined Acetonitrile: A Critical Examination of Two-State Models

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• 作者：Cassandra D. Norton ; Ward H. Thompson
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：July 17, 2014
• 年：2014
• 卷：118
• 期：28
• 页码：8227-8235
• 全文大小：403K
• ISSN：1520-5207

文摘

Molecular dynamics simulations are used to investigate the reorientation dynamics of liquid acetonitrile confined within a nanoscale, hydrophilic silica pore. The dynamics are strongly modified relative to the bulk liquid鈥攖he time scale for reorientation is increased by orders-of-magnitude and the dynamics become nonexponential鈥攁nd these effects are examined at the molecular level. In particular, commonly invoked two-state (or core鈥搒hell) models, with and without consideration of exchange of molecules between the states, are applied and discussed. A rigorous decomposition of the acetonitrile reorientational correlation function is introduced that permits the approximations implicit in the two-state models to be identified and tested systematically. The results show that exchange is an important component of the nanoconfined acetonitrile reorientation dynamics and a two-state model with exchange can accurately describe the correlation. However, the faithfulness of the model is related to the separation of time scales in the two states, which exists for a wide range of definitions of the two states. This suggests that caution should be exercised when inferring molecular-level details from application of two-state models.