Zum Stoßmechanismus bimolekularer Reaktionen: Teil I: Theorie und experimentelle Methode zur Bestimmung des Geschwindigkeitsspektrums der Produkte aus einfachen H‐Übertragungsreaktionen vom Typ X+ + H2 → XH+ + H

Henglein, A.; Lacmann, K.; Jacobs, G.

doi:10.1002/bbpc.19650690404

Cited by 87 publications

(4 citation statements)

References 10 publications

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“…For rebound, the XCH 3 product rebounds off the Y atom, scattering in the backward direction. For stripping, 35 X − strips CH 3 away from the Y atom with the XCH 3 product scattering in the forward direction. Frontside attack occurs without CH 3 inversion, with X − directly displacing Y − .…”

Section: Atomic-level Reaction Mechanismsmentioning

confidence: 99%

Identification of Atomic-Level Mechanisms for Gas-Phase X^– + CH₃Y S_N2 Reactions by Combined Experiments and Simulations

et al. 2014

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For the traditional model of gas-phase X(-) + CH3Y SN2 reactions, C3v ion-dipole pre- and postreaction complexes X(-)---CH3Y and XCH3---Y(-), separated by a central barrier, are formed. Statistical intramolecular dynamics are assumed for these complexes, so that their unimolecular rate constants are given by RRKM theory. Both previous simulations and experiments have shown that the dynamics of these complexes are not statistical and of interest is how these nonstatistical dynamics affect the SN2 rate constant. This work also found there was a transition from an indirect, nonstatistical, complex forming mechanism, to a direct mechanism, as either the vibrational and/or relative translational energy of the reactants was increased. The current Account reviews recent collaborative studies involving molecular beam ion-imaging experiments and direct (on-the-fly) dynamics simulations of the SN2 reactions for which Cl(-), F(-), and OH(-) react with CH3I. Also considered are reactions of the microsolvated anions OH(-)(H2O) and OH(-)(H2O)2 with CH3I. These studies have provided a detailed understanding of the atomistic mechanisms for these SN2 reactions. Overall, the atomistic dynamics for the Cl(-) + CH3I SN2 reaction follows those found in previous studies. The reaction is indirect, complex forming at low reactant collision energies, and then there is a transition to direct reaction between 0.2 and 0.4 eV. The direct reaction may occur by rebound mechanism, in which the ClCH3 product rebounds backward from the I(-) product or a stripping mechanism in which Cl(-) strips CH3 from the I atom and scatters in the forward direction. A similar indirect to direct mechanistic transition was observed in previous work for the Cl(-) + CH3Cl and Cl(-) + CH3Br SN2 reactions. At the high collision energy of 1.9 eV, a new indirect mechanism, called the roundabout, was discovered. For the F(-) + CH3I reaction, there is not a transition from indirect to direct reaction as Erel is increased. The indirect mechanism, with prereaction complex formation, is important at all the Erel investigated, contributing up ∼60% of the reaction. The remaining direct reaction occurs by the rebound and stripping mechanisms. Though the potential energy curve for the OH(-) + CH3I reaction is similar to that for F(-) + CH3I, the two reactions have different dynamics. They are akin, in that for both there is not a transition from an indirect to direct reaction. However, for F(-) + CH3I indirect reaction dominates at all Erel, but it is less important for OH(-) + CH3I and becomes negligible as Erel is increased. Stripping is a minor channel for F(-) + CH3I, but accounts for more than 60% of the OH(-) + CH3I reaction at high Erel. Adding one or two H2O molecules to OH(-) alters the reaction dynamics from that for unsolvated OH(-). Adding one H2O molecule enhances indirect reaction at low Erel, and changes the reaction mechanism from primarily stripping to rebound at high Erel. With two H2O molecules the dynamics is indirect and isotropic at all collision energies.

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Section: Atomic-level Reaction Mechanismsmentioning

confidence: 99%

Identification of Atomic-Level Mechanisms for Gas-Phase X^– + CH₃Y S_N2 Reactions by Combined Experiments and Simulations

et al. 2014

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“…The rotational energy of the assumed linear complex necessary to conserve angular momentum is and this energy is not available for flow through the vibrational modes. The nonfixed energy of SiH3CH2CH2+* is then a function of the impact parameter and is given by (1)(2)(3)(4)(5) where D2 is the exothermicity of formation of SiH3CH2CHz+ (cf. Figure 5).…”

Section: Theoretical Rates Of Collision Complex Decompositionmentioning

confidence: 99%

Persistent collision complexes in the reaction of silyl ions with ethylene

Allen¹,

Lampe²

1977

J. Am. Chem. Soc.

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The reaction of SiH3+ with C2H4 has been studied in a tandem mass spectrometer at relative kinetic energies in the range of 0.47 to 2.4 eV and at C2H4 pressures in the range of 2-80 X Torr. At low relative kinetic energies persistent collision complexes SiC2H7+ are directly observed, in the absence of collisional stabilization, some 2 X s after formation. Collisional stabilization by C2H4 increases the yield of SiC2H7+ so that at 80 X Torr this ion accounts for -80% of the observed products. The other observed products are SiQHS+, SiCH3+, and SiC2H3+. Extrapolation of product yields to infinite pressure indicates that the collision complex accounts for -90% of total reaction with the other 10% of reaction being due to a direct process forming SiCH3+. The experimental data yield absolute values for the lifetime of energy-rich collision complexes, for the unimolecular rate constants for decomposition of the complex to SiC*H5+ and SiCH3+, and for the single-collision stabilization of SiC2H7+* by C2H4. The strong collision assumption breaks down at the higher relative kinetic energies and a value of 0.7-1.1 eV for the maximum energy transferred per collision from SiC2H7+* to C2H4 may be derived. RRKM calculations based on the chemically activated molecule being CH3CH2SiH2+ and in which angular momentum of reactants is conserved give order-of-magnitude agreement with experiment.

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“…3 falls quite close to Qss, the value predicted by the simple spectator-stripping SS mode1. 23 For relative energies higher than 5 eV, Qmp levels off at a roughly constant value that is less negative than Qss. At high initial relative energies, therefore, the product NO+ is observed to have higher velocity than that predicted by SS.…”

Section: A Qualitativementioning

confidence: 98%

Crossed-Beam Study of the Reaction N++O2→NO++O

Tully

Herman

Wolfgang

1971

The Journal of Chemical Physics

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The reaction N++O2→NO++O has been studied as a function of collision energy using the crossed-beam apparatus EVA. This process is of considerable importance in the upper atmosphere. The system is also of particular interest because it may involve strong interactions between several intersecting or close-lying electronic surfaces of NO2+. This is not the case for previously well-studied ion–molecule reactions (e.g., Ar++D2), the dynamics of which are closely represented by simple models dominated by long-range electrostatic forces (e.g., “polarization stripping”). Beams of N+ in the ground (3P) state were crossed with thermal O2 beams and the angular and velocity distributions of the NO+ product measured. The reaction exhibits the asymmetric distribution characteristic of a direct process. Its translational exoergicity (Q) declines with energy, but above 5 eV relative energy, becomes constant. These data were then corrected for angular and energy spreads of the beams. The position of the plateau in Q appears consistent only with production of O(3P) and a state of NO+ which, with excess energy, dissociates to N(4S0) and O+(4S0). Consideration of the correlation diagram for NO2+ then indicates the following mechanism as probable: at moderately large separation N+(3P) and O2(3Σg+), originally on a surface correlating with linear NO2+ (excited Σ+1), experience on electron jump leading to a surface correlating similarly with NO2+ (1Σ−orΠ)1. Upon closer approach an O atom is transferred leading adiabatically to O(3P)+NO+(3Σ+). [The latter will dissociate to N(4S0) and O+(4S0) if sufficient energy is available.] Unlike the reaction to give ground-state products, this process is only slightly exoergic. This accounts for the fact that so little of the potentially available energy appears as translation.

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Zum Stoßmechanismus bimolekularer Reaktionen: Teil I: Theorie und experimentelle Methode zur Bestimmung des Geschwindigkeitsspektrums der Produkte aus einfachen H‐Übertragungsreaktionen vom Typ X⁺ + H₂ → XH⁺ + H

Cited by 87 publications

References 10 publications

Identification of Atomic-Level Mechanisms for Gas-Phase X^– + CH₃Y S_N2 Reactions by Combined Experiments and Simulations

Identification of Atomic-Level Mechanisms for Gas-Phase X^– + CH₃Y S_N2 Reactions by Combined Experiments and Simulations

Persistent collision complexes in the reaction of silyl ions with ethylene

Crossed-Beam Study of the Reaction N++O2→NO++O

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Zum Stoßmechanismus bimolekularer Reaktionen: Teil I: Theorie und experimentelle Methode zur Bestimmung des Geschwindigkeitsspektrums der Produkte aus einfachen H‐Übertragungsreaktionen vom Typ X+ + H2 → XH+ + H

Cited by 87 publications

References 10 publications

Identification of Atomic-Level Mechanisms for Gas-Phase X– + CH3Y SN2 Reactions by Combined Experiments and Simulations

Identification of Atomic-Level Mechanisms for Gas-Phase X– + CH3Y SN2 Reactions by Combined Experiments and Simulations

Persistent collision complexes in the reaction of silyl ions with ethylene

Crossed-Beam Study of the Reaction N++O2→NO++O

Contact Info

Product

Resources

About

Zum Stoßmechanismus bimolekularer Reaktionen: Teil I: Theorie und experimentelle Methode zur Bestimmung des Geschwindigkeitsspektrums der Produkte aus einfachen H‐Übertragungsreaktionen vom Typ X⁺ + H₂ → XH⁺ + H

Identification of Atomic-Level Mechanisms for Gas-Phase X^– + CH₃Y S_N2 Reactions by Combined Experiments and Simulations

Identification of Atomic-Level Mechanisms for Gas-Phase X^– + CH₃Y S_N2 Reactions by Combined Experiments and Simulations