Production of H and O( 3P) atoms in the reaction of CH 2 with O 2

Pei Fang Lee, Hiroyuki Matsui*, Wei Yu Chen, Niann-Shiah Wang

*Corresponding author for this work

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

The reaction CH 2 + O 2 → products has been studied by using atomic resonance absorption spectrometry (ARAS) of H and O( 3P) atoms behind reflected shock waves over 1850-2050 K and 2.1-1.7 atm. Measurements of [H] and [O] are conducted using mixtures of highly diluted CH 2I 2 (0.2 and 0.4 ppm) with excess O 2 (100 and 262 ppm) in Ar; comparative measurement of [H] in the 0.2 and 0.4 ppm CH 2I 2 + 300 ppm H 2 mixture has been conducted simultaneously to confirm the initial concentration of CH 2. The apparent reaction rate of CH 2 + O 2 (k 2′), including the contributions of 3CH 2 + O 2 → products (2) and 1CH 2 + O 2 → products (3), has been measured from the evolutions of [H] and [O] and summarized as k 2′/cm 3 molecule -1 s -1 = (1.90 ± 0.31) × 10 -11. The contribution of 1CH 2 + O 2 reaction on the measured k 2′ has been evaluated as 0.15 ± 0.04, with an assumption that k 3 is independent of temperature and given by the result measured at room temperature [Langford, A. O.; Petek, H.; Moore, C. B. J. Chem. Phys. 1983, 78, 6650-6659]. The net rate for the 3CH 2 + O 2 reaction is given as k 2/cm 3 molecule -1 s -1 = (1.69 ± 0.31) × 10 -11. The result on k 2 in this study is found to be consistent with the extrapolation of the previous work at lower temperature range of 295-600 K. [Vinckler, C.; Debruyn, W. J. Phys. Chem. 1979, 83, 2057-2062]; these results can be summarized as k 2/cm 3molecule -1 s -1 = 2.74 × 10 -11 exp(-874/T), (T = 295-2050 K). The apparent production yields of H and O atoms for the reaction channels 1,3CH 2 + O 2 → H + products (2a, 3a) and 1,3CH 2 + O 2 → O( 3P) + products (2b, 3b) have been evaluated as φ 2a′ = 0.59 ± 0.06 and φ 2b′ = 0.23 ± 0.06, respectively. The contributions of 1CH 2 + O 2 reaction on measured φ 2a′ and φ 2b′ are indicated to be minor; the net branching fractions for the 3CH 2+O 2 reaction are estimated as φ 2a = 0.58 ± 0.06 and φ 2b = 0.25 ± 0.06. No obvious temperature dependence is indicated in the measured rate constant nor in the branching fractions of H and O atoms. The mechanism of the reaction of CH 2 with O 2 is discussed based on the result of the present study together with those of the previous theoretical/experimental studies.

Original languageEnglish
Pages (from-to)9245-9254
Number of pages10
JournalJournal of Physical Chemistry A
Volume116
Issue number37
DOIs
StatePublished - 20 Sep 2012

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