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Title: Solvent Exchange in Liquid Methanol and Rate Theory

Abstract

To enhance our understanding of the solvent exchange mechanism in liquid methanol, we report a systematic study of this process using molecular dynamics simulations. We use transition state theory, the Impey-Madden-McDonald method, the reactive flux method, and Grote-Hynes theory to compute the rate constants for this process. Solvent coupling was found to dominate, resulting in a significantly small transmission coefficient. We predict a positive activation volume for the methanol exchange process. The essential features of the dynamics of the system as well as the pressure dependence are recovered from a Generalized Langevin Equation description of the dynamics. We find that the dynamics and response to anharmonicity can be decomposed into two time regimes, one corresponding to short time response (< 0.1 ps) and long time response (> 5 ps). An effective characterization of the process results from launching dynamics from the planar hypersurface corresponding to Grote-Hynes theory. This results in improved numerical convergence of correlation functions. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.

Authors:
;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1239470
Report Number(s):
PNNL-SA-113185
Journal ID: ISSN 0009-2614; KC0301050
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Chemical Physics Letters; Journal Volume: 643
Country of Publication:
United States
Language:
English

Citation Formats

Dang, Liem X., and Schenter, Gregory K.. Solvent Exchange in Liquid Methanol and Rate Theory. United States: N. p., 2016. Web. doi:10.1016/j.cplett.2015.10.045.
Dang, Liem X., & Schenter, Gregory K.. Solvent Exchange in Liquid Methanol and Rate Theory. United States. doi:10.1016/j.cplett.2015.10.045.
Dang, Liem X., and Schenter, Gregory K.. Fri . "Solvent Exchange in Liquid Methanol and Rate Theory". United States. doi:10.1016/j.cplett.2015.10.045.
@article{osti_1239470,
title = {Solvent Exchange in Liquid Methanol and Rate Theory},
author = {Dang, Liem X. and Schenter, Gregory K.},
abstractNote = {To enhance our understanding of the solvent exchange mechanism in liquid methanol, we report a systematic study of this process using molecular dynamics simulations. We use transition state theory, the Impey-Madden-McDonald method, the reactive flux method, and Grote-Hynes theory to compute the rate constants for this process. Solvent coupling was found to dominate, resulting in a significantly small transmission coefficient. We predict a positive activation volume for the methanol exchange process. The essential features of the dynamics of the system as well as the pressure dependence are recovered from a Generalized Langevin Equation description of the dynamics. We find that the dynamics and response to anharmonicity can be decomposed into two time regimes, one corresponding to short time response (< 0.1 ps) and long time response (> 5 ps). An effective characterization of the process results from launching dynamics from the planar hypersurface corresponding to Grote-Hynes theory. This results in improved numerical convergence of correlation functions. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.},
doi = {10.1016/j.cplett.2015.10.045},
journal = {Chemical Physics Letters},
number = ,
volume = 643,
place = {United States},
year = {Fri Jan 01 00:00:00 EST 2016},
month = {Fri Jan 01 00:00:00 EST 2016}
}
  • NMR studies of methyl borate in methanol solution indicate fast methoxyl exchange with a large deuterium solvent isotope effect: k/sub CH/sub 3/OH//k/sub CH/sub 3/OD/ = 11.0 at 25/sup 0/C. The temperature dependence of the first-order rate constants (s/sup -1/) is given by k/sub CH/sub 3/OH/ = 5.7 x 10/sup 3/ e/sup -2360/RT/ and k/sub CH/sub 3/OD/ = 9.1 x 10/sup 3/ e/sup -4060/RT/. These constants refer to a pH-independent phase of the exchange. Catalysis by lyonium and lyate ions occurs with approximate rate constants (M/sup -1/ s/sup -1/) k/sub CH/sub 3/OH/sub 2//sup +// = 1.4 x 10/sup 5/, k/sub CH/submore » 3/OD/sub 2//sup +// = 1.0 x 10/sup 5/, and k/sub CH/sub 3/O/sup -// = 7 x 10/sup 10/. 4 figs.« less
  • In this paper, we describe our efforts to apply rate theories in studies of solvent exchange around Li +(aq) and the kinetics of ion pairings in lithium-ion batteries (LIB). We report one of the first computer simulations of the exchange dynamics around hydrated Li + in acetonitrile (ACN), which is common solvent used in LIBs. We also provide details of the ion-pairing kinetics of Li +-[BF 4] and Li +-[PF 6] in ACN. Using our polarizable force-field models and employing classical rate theories of chemical reactions, we examine the ACN exchange process between the first and second solvation shells aroundmore » Li +(aq). We calculate exchange rates using transition state theory and weighted them with transmission coefficients determined by the reactive flux and Impey, Madden, and McDonald approaches and Grote-Hynes theory. We found the relaxation times changed from 180 ps to 4600 ps and from 30 ps to 280 ps for Li +-[BF 4] and Li +-[PF 6] ion pairs, respectively. These results confirm that the solvent response to the kinetics of ion pairing is significant. Our results also show that, in addition to affecting the free energy of solvation into ACN, the anion type also should significantly influence the kinetics of ion pairing. These results will increase our understanding of the thermodynamic and kinetic properties of LIB systems.« less
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