The nonstatistical dissociation dynamics of chloride(bromomethane) Cl-(CH3Br): evidence for vibrational excitation in the products of gas-phase SN2 reactions

Graul, Susan T.; Bowers, Michael T.

doi:10.1021/ja00025a058

Cited by 108 publications

(81 citation statements)

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“…In summary, for reaction out of CH 3 Br in its vibrational ground state, products with the C-Cl stretch excited by 2-4 quanta are formed. In agreement with the observation by Graul and Bowers,42,43 the products are vibrationally hot.…”

Section: The Exothermic Reaction CL − +Ch 3 Brsupporting

confidence: 91%

Four-dimensional quantum study on exothermic complex-forming reactions: Cl−+CH3Br→ClCH3+Br−

Hennig

Schmatz

2005

The Journal of Chemical Physics

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The exothermic gas-phase bimolecular nucleophilic substitution (S(N)2) reaction Cl(-)+CH(3)Br (upsilon1',upsilon2',upsilon3')-->ClCH(3) (upsilon1,upsilon2,upsilon3)+Br- and the corresponding endothermic reverse reaction have been studied by time-independent quantum scattering calculations in hyperspherical coordinates on a coupled-cluster potential-energy surface. The dimensionality-reduced model takes four degrees of freedom into account [Cl-C and C-Br stretching modes (quantum numbers upsilon3' and upsilon3); totally symmetric modes of the methyl group, i.e., C-H stretching (upsilon1' and upsilon1) and umbrella bending vibrations (upsilon2' and upsilon2)]. Diagonalization of the Hamiltonian was performed employing the Lanczos algorithm with a variation of partial reorthogonalization. A narrow grid in the total energy was employed so that long-living resonance states could be resolved and extracted. While excitation of the reactant umbrella bending mode already leads to a considerable enhancement of the reaction probability, its combination with vibrational excitation of the broken C-Br bond, (0, 1, 1), results in a strong synergic effect that can be rationalized by the similarity with the classical transitional normal mode. Exciting the C-H stretch has a non-negligible effect on the reaction probability, while for larger translational energies this mode follows the expected spectatorlike behavior. Combination of C-Br stretch and symmetric C-H, (1,0,1), stretch does not show a cooperative effect. Contrary to the spectator mode concept, energy originally stored in the C-H stretching mode is by no means conserved, but almost completely released in other modes of the reaction products. Products are most likely formed in states with a high degree of excitation in the new C-Cl bond, while the internal modes of the methyl group are less important. Reactants with combined umbrella/C-Br stretch excitation, (0, 1, 1), may yield products with two quanta in the umbrella mode.

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Section: The Exothermic Reaction CL − +Ch 3 Brsupporting

confidence: 91%

Four-dimensional quantum study on exothermic complex-forming reactions: Cl−+CH3Br→ClCH3+Br−

Hennig

Schmatz

2005

The Journal of Chemical Physics

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“…Recent theoretical and experirnental work o n gas-phase S,2 reactions has questioned the principal assumptions of statistical theories (13)(14)(15)(16), especially that of corn- Fig. 2.…”

Section: Perturbed Equilibria and Statistical Energy Redistribution Imentioning

confidence: 99%

“…The short lifetimes are a result of the small size and lo\\, association energies (-10 kcal tnolp') (14,19) of halide-methyl halide complexes, which are not typical of many ion-molecule reactions. The association energy of [C1.C1CH2CNI-, for example, is -19 kcal tnolp' (10).…”

Section: Perturbed Equilibria and Statistical Energy Redistribution Imentioning

confidence: 99%

Perturbed Equilibria and Statistical Energy Redistribution in a Gas-Phase S _N 2 Reaction

Craig

Brauman

1997

Science

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The relative translational energy of one set of reactants in the gas-phase equilibrium between chloride ion and chloroacetonitrile 35 Cl − + 37 ClCH 2 CN ⇌ 37 Cl − + 35 ClCH 2 CN is varied without affecting the energy distribution of the other set. The steady-state ratio of ionic isotopes changes so that there is an increase in the concentration of energized reactants. The ratio provides a measure of the translational energy dependence of the rate constant for the bimolecular nucleophilic substitution (S N 2) reaction. The observed energy dependence is indistinguishable from that predicted by Rice-Ramsperger-Kassel-Marcus theory, suggesting that the increased translational energy redistributes statistically in the collision complex.

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“…6,10,13,14,16 This reaction is thought to proceed along a double-well potential energy surface with a central barrier that separates the entrance and exit channel ion complexes. Both of these reaction complexes have been shown to behave in distinctly nonstatistical manners and, therefore, are not well-described by conventional statistical theories of reaction rates, such as RRKM theory.…”

Section: Introductionmentioning

confidence: 99%

Rate Constants for the Gas Phase Reaction of Chloride Ion with Methyl Bromide over the Pressure Range 300 to 1100 Torr

1997

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Rate constants for the reaction of chloride ion with methyl bromide have been determined over a range of buffer gas pressures from 300 to 1100 Torr at 125°C by ion mobility spectrometry (IMS). The rate constants were found to increase slightly with increased pressure over this range and also increased slightly with a change from nitrogen to methane buffer gas. Parallel measurements for the reaction of chloride ion with n-butyl bromide indicated no dependence of the observed rate constants on changes in the pressure or identity of the buffer gas, as expected. The present measurements indicate that the high-pressure limit (HPL) of kinetic behavior is not achieved for the Cl -/CH 3 Br reaction system by use of buffer gases in the near-atmospheric pressure range and are consistent with a recent suggestion by Seeley et al. that this reaction should occur with near-collision frequency in its high-pressure limit.

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The nonstatistical dissociation dynamics of chloride(bromomethane) Cl-(CH3Br): evidence for vibrational excitation in the products of gas-phase SN2 reactions

Cited by 108 publications

References 0 publications

Four-dimensional quantum study on exothermic complex-forming reactions: Cl−+CH3Br→ClCH3+Br−

Four-dimensional quantum study on exothermic complex-forming reactions: Cl−+CH3Br→ClCH3+Br−

Perturbed Equilibria and Statistical Energy Redistribution in a Gas-Phase S _N 2 Reaction

Rate Constants for the Gas Phase Reaction of Chloride Ion with Methyl Bromide over the Pressure Range 300 to 1100 Torr

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The nonstatistical dissociation dynamics of chloride(bromomethane) Cl-(CH3Br): evidence for vibrational excitation in the products of gas-phase SN2 reactions

Cited by 108 publications

References 0 publications

Four-dimensional quantum study on exothermic complex-forming reactions: Cl−+CH3Br→ClCH3+Br−

Four-dimensional quantum study on exothermic complex-forming reactions: Cl−+CH3Br→ClCH3+Br−

Perturbed Equilibria and Statistical Energy Redistribution in a Gas-Phase S N 2 Reaction

Rate Constants for the Gas Phase Reaction of Chloride Ion with Methyl Bromide over the Pressure Range 300 to 1100 Torr

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Perturbed Equilibria and Statistical Energy Redistribution in a Gas-Phase S _N 2 Reaction