| Autor: |
Speak TH; School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K., Blitz MA; School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.; National Centre for Atmospheric Science, University of Leeds, Leeds LS2 9JT, U.K., Medeiros DJ; School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K., Seakins PW; School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K. |
| Jazyk: |
angličtina |
| Zdroj: |
JACS Au [JACS Au] 2023 Jun 06; Vol. 3 (6), pp. 1684-1694. Date of Electronic Publication: 2023 Jun 06 (Print Publication: 2023). |
| DOI: |
10.1021/jacsau.3c00110 |
| Abstrakt: |
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 HO 2 radicals, monitoring OH by laser-induced fluorescence using two different approaches, looking at the direct reaction and also the perturbation of the slow OH + H 2 O 2 reaction with radical concentration, and over a wide range of pressures. Both approaches give a consistent measurement of k 1,298K ∼1 × 10 -11 cm 3 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,H 2 O, 298K = (2.17 ± 0.09) × 10 -28 cm 6 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 + HO 2 → HCl + O 2 . The implications of these results in atmospheric models are discussed.
Competing Interests: The authors declare no competing financial interest.
(© 2023 The Authors. Published by American Chemical Society.) |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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