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Title: Nonthermal rate constants for CH4* + X → CH3 + HX, X = H, O, OH, and O2

Journal Article · · Journal of Chemical Physics
DOI:https://doi.org/10.1063/1.5090394· OSTI ID:1510465
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Argonne National Lab. (ANL), Argonne, IL (United States)
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Quasiclassical trajectories are essential to compute nonthermal rate constants, k*, for abstraction reactions involving highly-excited methane CH4* and the radicals H, O, OH, and O2. Several temperatures and internal energies of methane, Evib, are observed, and significant nonthermal rate enhancements for large Evib are found. Specifically, when CH4* is internally excited close to its dissociation threshold (Evib approximate to D0 = 104 kcal/mol), its reactivity with H, O, and OH is shown to be collision-rate-limited and to approach that of comparably-sized radicals, such as CH3, with k* > 10-10 cm3 molecule-1 s-1. Rate constants this large are more typically associated with barrierless reactions, and at 1000 K, this represents a nonthermal rate enhancement, k*/k, of more than two orders of magnitude relative to thermal rate constants k. We show that large nonthermal rate constants persist even after significant internal cooling, with k*/k > 10 down to Evib approximate to D0/4. The competition among collisional cooling and nonthermal reactivity is studied using a simple model, and nonthermal reactions are shown to account for up to 35%-50% of the fate of the products of H + CH3 = CH4* under conditions of practical relevance to combustion. Lastly, the accuracy of an effective temperature model for estimating k* from k is quantified.

Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
Grant/Contract Number:
AC02-06CH11357; FWP 59044
OSTI ID:
1510465
Alternate ID(s):
OSTI ID: 1502269
Journal Information:
Journal of Chemical Physics, Vol. 150, Issue 11; ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 19 works
Citation information provided by
Web of Science

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