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Title: Experimental and theoretical rate constants for CH{sub 4} + O{sub 2} {yields} CH{sub 3} + HO{sub 2}

Abstract

In this study, rate constants for the primary initiation process in low to moderate temperature CH{sub 4} oxidation CH{sub 4} + O{sub 2} {yields} CH{sub 3} + HO{sub 2} have been measured in a reflected shock tube apparatus between 1655 and 1822 K using multipass absorption spectrometric detection of OH radicals at 308 nm. After rapid dissociation of HO{sub 2} yielding H atoms, which are instantaneously converted to OH by H + O{sub 2} {yields} OH + O, the temporal concentration of OH radicals was observed as the final product from the rate-controlling title reaction. The present work utilizes 18 optical passes corresponding to a total path length of 1.6 m. This configuration gives a signal to noise ratio of unity at {proportional_to}3 x 10{sup 12} radicals cm{sup -3}. Hence, kinetics experiments could be performed at conditions of low [CH{sub 4}]{sub 0} (60-70 ppm), thereby substantially reducing secondary chemistry. Possible implications of CH{sub 4} dissociation contributing to the OH formation rates were considered. The present experimental results agree with a priori variational transition state theoretical (VTST) calculations, k{sub th}=3.37 x 10{sup -19}T{sup 2.745} exp (-26,041K/T)cm{sup 3}molecule{sup -1} s{sup -1}, clearly showing overlap of experiment and theory, within experimental error. Themore » new rate constant values obtained in this study are 8-10 times higher than the values used in the popular mechanisms GRI-Mech 3.0 and Leeds Methane Mechanism, version 1.5. (author)« less

Authors:
; ; ;  [1]
  1. Chemistry Division, Argonne National Laboratory, Argonne, IL 60439 (United States)
Publication Date:
OSTI Identifier:
20880642
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 149; Journal Issue: 1-2; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; METHANE; METHYL RADICALS; HYDROXYL RADICALS; CHEMICAL REACTION KINETICS; VARIATIONAL METHODS; SIGNAL-TO-NOISE RATIO; DISSOCIATION; OXIDATION; ABSORPTION; TEMPERATURE RANGE 1000-4000 K; OXYGEN

Citation Formats

Srinivasan, N.K., Michael, J.V., Harding, L.B., and Klippenstein, S.J.. Experimental and theoretical rate constants for CH{sub 4} + O{sub 2} {yields} CH{sub 3} + HO{sub 2}. United States: N. p., 2007. Web. doi:10.1016/J.COMBUSTFLAME.2006.12.010.
Srinivasan, N.K., Michael, J.V., Harding, L.B., & Klippenstein, S.J.. Experimental and theoretical rate constants for CH{sub 4} + O{sub 2} {yields} CH{sub 3} + HO{sub 2}. United States. doi:10.1016/J.COMBUSTFLAME.2006.12.010.
Srinivasan, N.K., Michael, J.V., Harding, L.B., and Klippenstein, S.J.. Sun . "Experimental and theoretical rate constants for CH{sub 4} + O{sub 2} {yields} CH{sub 3} + HO{sub 2}". United States. doi:10.1016/J.COMBUSTFLAME.2006.12.010.
@article{osti_20880642,
title = {Experimental and theoretical rate constants for CH{sub 4} + O{sub 2} {yields} CH{sub 3} + HO{sub 2}},
author = {Srinivasan, N.K. and Michael, J.V. and Harding, L.B. and Klippenstein, S.J.},
abstractNote = {In this study, rate constants for the primary initiation process in low to moderate temperature CH{sub 4} oxidation CH{sub 4} + O{sub 2} {yields} CH{sub 3} + HO{sub 2} have been measured in a reflected shock tube apparatus between 1655 and 1822 K using multipass absorption spectrometric detection of OH radicals at 308 nm. After rapid dissociation of HO{sub 2} yielding H atoms, which are instantaneously converted to OH by H + O{sub 2} {yields} OH + O, the temporal concentration of OH radicals was observed as the final product from the rate-controlling title reaction. The present work utilizes 18 optical passes corresponding to a total path length of 1.6 m. This configuration gives a signal to noise ratio of unity at {proportional_to}3 x 10{sup 12} radicals cm{sup -3}. Hence, kinetics experiments could be performed at conditions of low [CH{sub 4}]{sub 0} (60-70 ppm), thereby substantially reducing secondary chemistry. Possible implications of CH{sub 4} dissociation contributing to the OH formation rates were considered. The present experimental results agree with a priori variational transition state theoretical (VTST) calculations, k{sub th}=3.37 x 10{sup -19}T{sup 2.745} exp (-26,041K/T)cm{sup 3}molecule{sup -1} s{sup -1}, clearly showing overlap of experiment and theory, within experimental error. The new rate constant values obtained in this study are 8-10 times higher than the values used in the popular mechanisms GRI-Mech 3.0 and Leeds Methane Mechanism, version 1.5. (author)},
doi = {10.1016/J.COMBUSTFLAME.2006.12.010},
journal = {Combustion and Flame},
number = 1-2,
volume = 149,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}