Role of the Recombination Channel in the Reaction between the HO and HO<sub>2</sub> Radicals

Badenes, María Paula; Tucceri, María E.; Cobos, Carlos

doi:10.1021/acs.jpca.6b10427

Cited by 11 publications

(2 citation statements)

References 51 publications

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“…15,18 Although reaction via the triplet state is dominant, the excited singlet state can play a role. Badenes et al 24 calculated a high barrier (56.8 kJ mol −1 ) from the HOOOH complex to the abstraction projects and hence only considered recombination. Recombination only plays a significant role at very high pressures.…”

Section: Oh H O H O Homentioning

confidence: 99%

New Measurements and Calculations on the Kinetics of an Old Reaction: OH + HO₂ → H₂O + O₂

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Medeiros

et al. 2023

JACS Au

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Literature rate coefficients for the prototypical radical–radical reaction at 298 K vary by close to an order of magnitude; such variations challenge our understanding of fundamental reaction kinetics. We have studied the title reaction at room temperature via the use of laser flash photolysis to generate OH and HO2 radicals, monitoring OH by laser-induced fluorescence using two different approaches, looking at the direct reaction and also the perturbation of the slow OH + H2O2 reaction with radical concentration, and over a wide range of pressures. Both approaches give a consistent measurement of k 1,298K ∼1 × 10–11 cm3 molecule–1 s–1, at the lowest limit of previous determinations. We observe, experimentally, for the first time, a significant enhancement in the rate coefficient in the presence of water, k 1,H2O, 298K = (2.17 ± 0.09) × 10–28 cm6 molecule–2 s–1, where the error is statistical at the 1σ level. This result is consistent with previous theoretical calculations, and the effect goes some way to explaining some, but not all, of the variation in previous determinations of k 1,298K. Supporting master equation calculations, using calculated potential energy surfaces at the RCCSD(T)-F12b/CBS//RCCSD/aug-cc-pVTZ and UCCSD(T)/CBS//UCCSD/aug-cc-pVTZ levels, are in agreement with our experimental observations. However, realistic variations in barrier heights and transition state frequencies give a wide range of calculated rate coefficients showing that the current precision and accuracy of calculations are insufficient to resolve the experimental discrepancies. The lower value of k 1,298K is consistent with experimental observations of the rate coefficient of the related reaction, Cl + HO2 → HCl + O2. The implications of these results in atmospheric models are discussed.

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Section: Oh H O H O Homentioning

confidence: 99%

New Measurements and Calculations on the Kinetics of an Old Reaction: OH + HO₂ → H₂O + O₂

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Blitz

Medeiros

et al. 2023

JACS Au

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“…These experiments have stimulated many theoretical investigations of the reaction pathway and kinetics. ,,− Very recently, a full-dimensional global PES for the ground triplet state of R1 was constructed from high-level ab initio data and the calculated k R1 was found to agree with experiment over a wide T range . The availability of this PES allows a detailed study of the reaction dynamics, including mode specificity.…”

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Mode Specificity in the OH + HO₂ → H₂O + O₂ Reaction: Enhancement of Reactivity by Exciting a Spectator Mode

et al. 2020

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A reaction typically involves a few active modes while the other modes are largely preserved throughout the reaction as spectators. Excitation of an active mode is expected to promote the reaction, but depositing energy in a spectator mode typically has no effect, because of the differing ability for energy flow to the reaction coordinate. In this work, we report a surprising case of mode specificity in a key radical–radical reaction OH + HO2 → H2O + O2, where such canonical expectations fail to hold. Despite its spectator nature, the vibrational excitation of the OH reactant is shown at low collision energies to enhance the reactivity significantly. This unique effect can be attributed to the increased attraction with HO2 due to the larger dipole of the stretched OH. At low collision energies, the stronger attraction increases the chance of capturing the reactants to form a hydrogen-bonded complex, thus of passing through the submerged barrier. The novel mechanism differs from the conventional vibrational enhancement via coupling to the reaction coordinate at the transition state, enriching our understanding of mode specificity in chemistry.

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Exploring unimolecular dissociation kinetics of ethyl dibromide through electronic structure calculations

Gulvi

Patel²,

Badani

2018

Chemical Physics

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Role of the Recombination Channel in the Reaction between the HO and HO₂ Radicals

Cited by 11 publications

References 51 publications

New Measurements and Calculations on the Kinetics of an Old Reaction: OH + HO₂ → H₂O + O₂

New Measurements and Calculations on the Kinetics of an Old Reaction: OH + HO₂ → H₂O + O₂

Mode Specificity in the OH + HO₂ → H₂O + O₂ Reaction: Enhancement of Reactivity by Exciting a Spectator Mode

Exploring unimolecular dissociation kinetics of ethyl dibromide through electronic structure calculations

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Role of the Recombination Channel in the Reaction between the HO and HO2 Radicals

Cited by 11 publications

References 51 publications

New Measurements and Calculations on the Kinetics of an Old Reaction: OH + HO2 → H2O + O2

New Measurements and Calculations on the Kinetics of an Old Reaction: OH + HO2 → H2O + O2

Mode Specificity in the OH + HO2 → H2O + O2 Reaction: Enhancement of Reactivity by Exciting a Spectator Mode

Exploring unimolecular dissociation kinetics of ethyl dibromide through electronic structure calculations

Contact Info

Product

Resources

About

Role of the Recombination Channel in the Reaction between the HO and HO₂ Radicals

New Measurements and Calculations on the Kinetics of an Old Reaction: OH + HO₂ → H₂O + O₂

New Measurements and Calculations on the Kinetics of an Old Reaction: OH + HO₂ → H₂O + O₂

Mode Specificity in the OH + HO₂ → H₂O + O₂ Reaction: Enhancement of Reactivity by Exciting a Spectator Mode