Study on the reaction of CH 2 with H 2 at high temperature

Pei Fang Lee, Hiroyuki Matsui*, Niann-Shiah Wang

*Corresponding author for this work

Research output: Contribution to journalArticle

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Abstract

Thermal decomposition of CH 2I 2 [sequential C-I bond fission processes, CH 2I 2 + Ar → CH 2I + I + Ar (1a) and CH 2I + Ar → 3CH 2 + I + Ar (1b)], and the reactions of 3CH 2 + H 2 → CH 3 + H (2) and 1CH 2 + H 2 → CH 3 + H (3) have been studied by using atomic resonance absorption spectrometry (ARAS) of I and H atoms behind reflected shock waves. Highly diluted CH 2I 2 (0.1-0.4 ppm) with/without excess H 2 (300 ppm) in Ar has been used so that the effect of the secondary reactions can be minimized. From the quantitative measurement of I atoms in the 0.1 ppm CH 2I 2 + Ar mixture over 1550-2010 K, it is confirmed that two-step sequential C-I bond fission processes of CH 2I 2, (1a) and (1b), dominate over other product channels. The decomposition step (1b) is confirmed to be the rate determining process to produce 3CH 2 and the least-squares analysis of the measured rate gives, ln(k 1b/cm 3 molecule -1 s -1) = -(17.28 ± 0.79) - (30.17 ± 1.40) × 10 3/T. By utilizing this result, we examine reactions 2 and 3 by monitoring evolution of H atoms in the 0.2-0.4 ppm CH 2I 2 + 300 ppm H 2 mixtures over 1850-2040 K. By using a theoretical result on k 2 (Lu, K. W.; Matsui, H.; Huang, C.-L.; Raghunath, P.; Wang, N.-S.; Lin, M. C.J. Phys. Chem. A 2010, 114, 5493), we determine the rate for (3) as k 3/cm 3 molecule -1 s -1 = (1.27 ± 0.36) × 10 -10. The upper limit of k 3 (k 3max) is also evaluated by assuming k 2 = 0, i.e., k 3max/cm 3 molecule -1 s -1 = (2.26 ± 0.59) × 10 -10. The present experimental results on k 3 and k 3max is found to agree very well with the previous frequency modulation spectroscopy study (Friedrichs, G.; Wagner, H. G.Z. Phys. Chem. 2001, 215, 1601); i.e., the importance of the contribution of 1CH 2 in the reaction of CH 2 with H 2 at elevated temperature range is reconfirmed.

Original languageEnglish
Pages (from-to)1891-1896
Number of pages6
JournalJournal of Physical Chemistry A
Volume116
Issue number8
DOIs
StatePublished - 1 Mar 2012

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