Product Branching from the CH<sub>2</sub>CH<sub>2</sub>OH Radical Intermediate of the OH + Ethene Reaction

Ratliff, Britni J.; Alligood, Bridget W.; Butler, Laurie J.; Lee, Shih‐Huang; Lin, Jim J.

doi:10.1021/jp203127k

Cited by 24 publications

(63 citation statements)

References 34 publications

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“…The resulting angular momenta were used to predict the portions of the total P(E T ) corresponding to stable and unstable radicals, which agreed quite well with the experimentally measured speeds of the stable radicals. In these experiments, an unexpectedly high branching to the vinyl + H 2 O channel was observed 21,22 in comparison to the expected branching to OH + ethene (the lowest barrier dissociation channel). The vinyl + H 2 O channel was proposed to occur via a "frustrated" dissociation or "roaming" pathway by Kamarchik et al 23 who performed quasiclassical trajectory calculations on vibrationally excited β-hydroxyethyl radicals.…”

Section: Introductionmentioning

confidence: 75%

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates

Brynteson

Butler

2015

The Journal of Chemical Physics

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We present a model which accurately predicts the net speed distributions of products resulting from the unimolecular decomposition of rotationally excited radicals. The radicals are produced photolytically from a halogenated precursor under collision-free conditions so they are not in a thermal distribution of rotational states. The accuracy relies on the radical dissociating with negligible energetic barrier beyond the endoergicity. We test the model predictions using previous velocity map imaging and crossed laser-molecular beam scattering experiments that photolytically generated rotationally excited CD2CD2OH and C3H6OH radicals from brominated precursors; some of those radicals then undergo further dissociation to CD2CD2 + OH and C3H6 + OH, respectively. We model the rotational trajectories of these radicals, with high vibrational and rotational energy, first near their equilibrium geometry, and then by projecting each point during the rotation to the transition state (continuing the rotational dynamics at that geometry). This allows us to accurately predict the recoil velocity imparted in the subsequent dissociation of the radical by calculating the tangential velocities of the CD2CD2/C3H6 and OH fragments at the transition state. The model also gives a prediction for the distribution of angles between the dissociation fragments' velocity vectors and the initial radical's velocity vector. These results are used to generate fits to the previously measured time-of-flight distributions of the dissociation fragments; the fits are excellent. The results demonstrate the importance of considering the precession of the angular velocity vector for a rotating radical. We also show that if the initial angular momentum of the rotating radical lies nearly parallel to a principal axis, the very narrow range of tangential velocities predicted by this model must be convoluted with a J = 0 recoil velocity distribution to achieve a good result. The model relies on measuring the kinetic energy release when the halogenated precursor is photodissociated via a repulsive excited state but does not include any adjustable parameters. Even when different conformers of the photolytic precursor are populated, weighting the prediction by a thermal conformer population gives an accurate prediction for the relative velocity vectors of the fragments from the highly rotationally excited radical intermediates.

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Section: Introductionmentioning

confidence: 75%

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates

Brynteson

Butler

2015

The Journal of Chemical Physics

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“…109 Photodissociation of nitrobenzene gives a bimodal distribution for the NO product. 108 A PES was constructed using CCSD/cc-pVDZ energies about the minima and B3LYP/cc-pVDZ energies for (>50,000) points along all exit channels.…”

Section: Roaming Mechanismmentioning

confidence: 99%

Organic Reaction Dynamics

Bachrach

2014

Computational Organic Chemistry

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In the previous chapters, we have focused our discussion of reaction mechanisms on the critical points along the reaction path. These critical points-local energy minima (reactants, intermediates, and products) and transition states (TSs)-were discussed in terms of their geometries and energies. We discussed the nature of the mechanism in terms of the topology of the potential energy surface (PES), the structure of the TSs, and the presence or absence of intermediates. We think of reactants progressing over TSs on to intermediates, perhaps through multiple intermediates and ending at products. This path is called the reaction coordinate and corresponds to the intrinsic reaction coordinate (IRC) or the minimum energy path (MEP) (see Section 1.6 for discussion on these two paths).This standard mechanistic analysis has a long successful history. Organic chemistry textbooks are filled with PESs and discussions of the implication of single-step versus multiple-step mechanisms, concerted TSs, and so on. 1,2 Transition state theory (TST) and Rice-Ramsperger-Kassel-Marcus (RRKM) theory provide tools for predicting rates based upon simple assumptions built upon the notion of reaction on the PES following the reaction coordinate. 3,4 An often-overlooked aspect of standard reaction mechanistic thought is that it really addresses only half of the picture. We talk about the positions of the atoms during the course of the reaction and the relative energies of points along the reaction path, but no mention is made of the time evolution of this process. In classical mechanics, description of a reactive system requires not just the particle positions but their momenta as well. The same is true for a quantum mechanical description, though one must keep in mind the limits imposed by the Heisenberg Uncertainty Principle. A complete description of a molecular reaction requires knowledge of both the position and the momentum of every atom for the entire time it takes for reactants to convert into products. This kind of description falls under the term molecular dynamics (MD).A few simple examples should suffice to demonstrate the critical role that MD plays in chemical reactions. Conservation of momentum must be enforced. Atoms and molecular fragments in motion must maintain their motion unless some barrier or force is applied to them. Consider the reaction of cis-2-butene with Computational Organic Chemistry, Second Edition. Steven M. Bachrach

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“…Under combustion conditions, CH 2 CH 2 OH may undergo a well‐known preferential OH‐elimination to ethylene + OH . This preference is energetically favored by a considerable amount, roughly 6 kcal/mol over the next likely possibility .…”

Section: Introductionmentioning

confidence: 99%

Master Equation Modeling of the Unimolecular Decompositions of α‐Hydroxyethyl (CH₃CHOH) and Ethoxy (CH₃CH₂O) Radicals

Dames

2014

Int J of Chemical Kinetics

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The unimolecular decomposition of two radical isomers of C2H5O (CH3CH2O/ethoxy, CH3CHOH/α‐hydroxyethyl) are investigated by means of Rice–Ramsperger–Kassel–Marcus/master equation simulations in helium and nitrogen bath gases on an accurate one‐dimensional potential energy surface. For ethoxy, simulations are carried out between temperatures of 406 and 1200 K and pressures of 0.001 and 100 atm. For CH3CHOH, simulations are carried out between temperatures of 800 and 1500 K and pressures of 0.001 and 100 atm. Results are compared with available experimental data, with good agreement. The dominant product of α‐hydroxyethyl decomposition is CH3CHO + H, with C2H3OH + H and CH3 + CH2O, being minor channels. Rate coefficients are strongly dependent on temperature and pressure and are recommended with attendant uncertainty factor estimates. The relative roles of vinyl alcohol and acetaldehyde in the context of combustion chemistry are also discussed.

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Product Branching from the CH₂CH₂OH Radical Intermediate of the OH + Ethene Reaction

Cited by 24 publications

References 34 publications

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates

Organic Reaction Dynamics

Master Equation Modeling of the Unimolecular Decompositions of α‐Hydroxyethyl (CH₃CHOH) and Ethoxy (CH₃CH₂O) Radicals

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Product Branching from the CH2CH2OH Radical Intermediate of the OH + Ethene Reaction

Cited by 24 publications

References 34 publications

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates

Organic Reaction Dynamics

Master Equation Modeling of the Unimolecular Decompositions of α‐Hydroxyethyl (CH3CHOH) and Ethoxy (CH3CH2O) Radicals

Contact Info

Product

Resources

About

Product Branching from the CH₂CH₂OH Radical Intermediate of the OH + Ethene Reaction

Master Equation Modeling of the Unimolecular Decompositions of α‐Hydroxyethyl (CH₃CHOH) and Ethoxy (CH₃CH₂O) Radicals