Study on the reaction of CH2 with H2 at high temperature.

Thermal decomposition of CH(2)I(2) [sequential C-I bond fission processes, CH(2)I(2) + Ar → CH(2)I + I + Ar (1a) and CH(2)I + Ar → (3)CH(2) + I + Ar (1b)], and the reactions of (3)CH(2) + H(2) → CH(3) + H (2) and (1)CH(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(2)I(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(2)I(2) + Ar mixture over 1550-2010 K, it is confirmed that two-step sequential C-I bond fission processes of CH(2)I(2), (1a) and (1b), dominate over other product channels. The decomposition step (1b) is confirmed to be the rate determining process to produce (3)CH(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(2)I(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 (1)CH(2) in the reaction of CH(2) with H(2) at elevated temperature range is reconfirmed.