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

Journal Article · Sun Apr 15 04:00:00 EDT 2007 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2006.12.010· OSTI ID:20880642

Srinivasan, N K; Michael, J V; Harding, L B; Klippenstein, S J ^[1]

---

1. Chemistry Division, Argonne National Laboratory, Argonne, IL 60439 (United States)

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)

• OSTI ID: 20880642
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 1-2 Vol. 149; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION
CHEMICAL REACTION KINETICS
DISSOCIATION
HYDROXYL RADICALS
METHANE
METHYL RADICALS
OXIDATION
OXYGEN
SIGNAL-TO-NOISE RATIO
TEMPERATURE RANGE 1000-4000 K
VARIATIONAL METHODS