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Title: Simulation studies of the Cl{sup -}+ CH{sub 3}I S{sub N}2 nucleophilic substitution reaction: Comparison with ion imaging experiments

Abstract

In the previous work of Mikosch et al.[Science 319, 183 (2008)], ion imaging experiments were used to study the Cl{sup -}+ CH{sub 3}I {yields} ClCH{sub 3}+ I{sup -} reaction at collision energies E{sub rel} of 0.39, 0.76, 1.07, and 1.9 eV. For the work reported here MP2(fc)/ECP/d direct dynamics simulations were performed to obtain an atomistic understanding of the experiments. There is good agreement with the experimental product energy and scattering angle distributions for the highest three E{sub rel}, and at these energies 80% or more of the reaction is direct, primarily occurring by a rebound mechanism with backward scattering. At 0.76 eV there is a small indirect component, with isotropic scattering, involving formation of the pre- and post-reaction complexes. All of the reaction is direct at 1.07 eV. Increasing E{sub rel} to 1.9 eV opens up a new indirect pathway, the roundabout mechanism. The product energy is primarily partitioned into relative translation for the direct reactions, but to CH{sub 3}Cl internal energy for the indirect reactions. The roundabout mechanism transfers substantial energy to CH{sub 3}Cl rotation. At E{sub rel}= 0.39 eV both the experimental product energy partitioning and scattering are statistical, suggesting the reaction is primarily indirect with formationmore » of the pre- and post-reaction complexes. However, neither MP2 nor BhandH/ECP/d simulations agree with experiment and, instead, give reaction dominated by direct processes as found for the higher collision energies. Decreasing the simulation E{sub rel} to 0.20 eV results in product energy partitioning and scattering which agree with the 0.39 eV experiment. The sharp transition from a dominant direct to indirect reaction as E{sub rel} is lowered from 0.39 to 0.20 eV is striking. The lack of agreement between the simulations and experiment for E{sub rel}= 0.39 eV may result from a distribution of collision energies in the experiment and/or a shortcoming in both the MP2 and BhandH simulations. Increasing the reactant rotational temperature from 75 to 300 K for the 1.9 eV collisions, results in more rotational energy in the CH{sub 3}Cl product and a larger fraction of roundabout trajectories. Even though a ClCH{sub 3}-I{sup -} post-reaction complex is not formed and the mechanistic dynamics are not statistical, the roundabout mechanism gives product energy partitioning in approximate agreement with phase space theory.« less

Authors:
 [1]; ; ;  [2];  [3];  [4]
  1. Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)
  2. Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061 (United States)
  3. National Research Council of Canada, Steacie Institute for Molecular Sciences, 100 Sussex Drive, Ottawa, Ontario K1AOR6 (Canada)
  4. Institut fur Ionenphysik und Angewandte Physik, Universitaet Innsbruck, Technikerstrasse 25/3, A-6020 Innsbruck (Austria)
Publication Date:
OSTI Identifier:
22105432
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 138; Journal Issue: 11; Other Information: (c) 2013 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CHLORINE IONS; COMPARATIVE EVALUATIONS; COMPLEXES; DIRECT REACTIONS; DISTRIBUTION; EV RANGE; IODINE IONS; ION-MOLECULE COLLISIONS; METHYL CHLORIDE; METHYL IODIDE; PHASE SPACE; REACTION KINETICS; ROTATIONAL STATES; SCATTERING; SIMULATION

Citation Formats

Jiaxu, Zhang, Lourderaj, Upakarasamy, Rui, Sun, Hase, William L., Mikosch, Jochen, and Wester, Roland. Simulation studies of the Cl{sup -}+ CH{sub 3}I S{sub N}2 nucleophilic substitution reaction: Comparison with ion imaging experiments. United States: N. p., 2013. Web. doi:10.1063/1.4795495.
Jiaxu, Zhang, Lourderaj, Upakarasamy, Rui, Sun, Hase, William L., Mikosch, Jochen, & Wester, Roland. Simulation studies of the Cl{sup -}+ CH{sub 3}I S{sub N}2 nucleophilic substitution reaction: Comparison with ion imaging experiments. United States. https://doi.org/10.1063/1.4795495
Jiaxu, Zhang, Lourderaj, Upakarasamy, Rui, Sun, Hase, William L., Mikosch, Jochen, and Wester, Roland. 2013. "Simulation studies of the Cl{sup -}+ CH{sub 3}I S{sub N}2 nucleophilic substitution reaction: Comparison with ion imaging experiments". United States. https://doi.org/10.1063/1.4795495.
@article{osti_22105432,
title = {Simulation studies of the Cl{sup -}+ CH{sub 3}I S{sub N}2 nucleophilic substitution reaction: Comparison with ion imaging experiments},
author = {Jiaxu, Zhang and Lourderaj, Upakarasamy and Rui, Sun and Hase, William L. and Mikosch, Jochen and Wester, Roland},
abstractNote = {In the previous work of Mikosch et al.[Science 319, 183 (2008)], ion imaging experiments were used to study the Cl{sup -}+ CH{sub 3}I {yields} ClCH{sub 3}+ I{sup -} reaction at collision energies E{sub rel} of 0.39, 0.76, 1.07, and 1.9 eV. For the work reported here MP2(fc)/ECP/d direct dynamics simulations were performed to obtain an atomistic understanding of the experiments. There is good agreement with the experimental product energy and scattering angle distributions for the highest three E{sub rel}, and at these energies 80% or more of the reaction is direct, primarily occurring by a rebound mechanism with backward scattering. At 0.76 eV there is a small indirect component, with isotropic scattering, involving formation of the pre- and post-reaction complexes. All of the reaction is direct at 1.07 eV. Increasing E{sub rel} to 1.9 eV opens up a new indirect pathway, the roundabout mechanism. The product energy is primarily partitioned into relative translation for the direct reactions, but to CH{sub 3}Cl internal energy for the indirect reactions. The roundabout mechanism transfers substantial energy to CH{sub 3}Cl rotation. At E{sub rel}= 0.39 eV both the experimental product energy partitioning and scattering are statistical, suggesting the reaction is primarily indirect with formation of the pre- and post-reaction complexes. However, neither MP2 nor BhandH/ECP/d simulations agree with experiment and, instead, give reaction dominated by direct processes as found for the higher collision energies. Decreasing the simulation E{sub rel} to 0.20 eV results in product energy partitioning and scattering which agree with the 0.39 eV experiment. The sharp transition from a dominant direct to indirect reaction as E{sub rel} is lowered from 0.39 to 0.20 eV is striking. The lack of agreement between the simulations and experiment for E{sub rel}= 0.39 eV may result from a distribution of collision energies in the experiment and/or a shortcoming in both the MP2 and BhandH simulations. Increasing the reactant rotational temperature from 75 to 300 K for the 1.9 eV collisions, results in more rotational energy in the CH{sub 3}Cl product and a larger fraction of roundabout trajectories. Even though a ClCH{sub 3}-I{sup -} post-reaction complex is not formed and the mechanistic dynamics are not statistical, the roundabout mechanism gives product energy partitioning in approximate agreement with phase space theory.},
doi = {10.1063/1.4795495},
url = {https://www.osti.gov/biblio/22105432}, journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 11,
volume = 138,
place = {United States},
year = {Thu Mar 21 00:00:00 EDT 2013},
month = {Thu Mar 21 00:00:00 EDT 2013}
}