Department of Applied Chemistry, National Chiao Tung University, 1001, Ta Hsueh Road, Hsinchu 30010, Taiwan.
J Phys Chem A. 2012 Mar 1;116(8):1891-6. doi: 10.1021/jp211849h. Epub 2012 Feb 21.
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.
CH(2)I(2)的热分解[连续的 C-I 键断裂过程，CH(2)I(2) + Ar → CH(2)I + I + Ar (1a) 和 CH(2)I + Ar → (3)CH(2) + I + Ar (1b)]，以及 (3)CH(2) + H(2) → CH(3) + H (2) 和 (1)CH(2) + H(2) → CH(3) + H (3)的反应，已经通过使用原子共振吸收光谱法 (ARAS) 在反射激波后研究了 I 和 H 原子。在 Ar 中使用高度稀释的 CH(2)I(2)（0.1-0.4 ppm）和/或过量的 H(2)（300 ppm），以最小化次级反应的影响。从定量测量 0.1 ppm CH(2)I(2) + Ar 混合物中 1550-2010 K 范围内的 I 原子，可以确认 CH(2)I(2)的两步连续 C-I 键断裂过程 (1a) 和 (1b) 主导着其他产物通道。分解步骤 (1b) 被确认为生成 (3)CH(2)的速率决定步骤，通过对测量速率进行最小二乘法分析，得到 ln(k(1b)/cm(3)分子(-1) s(-1)) = -(17.28 ± 0.79) - (30.17 ± 1.40) × 10(3)/T。利用这个结果，我们通过监测 0.2-0.4 ppm CH(2)I(2) + 300 ppm H(2)混合物中 H 原子的演变，在 1850-2040 K 范围内研究了反应 2 和 3。利用关于 k(2)的理论结果 (Lu, K. W.; Matsui, H.; Huang, C.-L.; Raghunath, P.; Wang, N.-S.; Lin, M. C. J. Phys. Chem. A 2010, 114, 5493)，我们确定了 (3)的速率为 k(3)/cm(3)分子(-1) s(-1) = (1.27 ± 0.36) × 10(-10)。还通过假设 k(2) = 0 来评估 k(3)的上限 (k(3max))，即 k(3max)/cm(3)分子(-1) s(-1) = (2.26 ± 0.59) × 10(-10)。实验结果表明，k(3)和 k(3max)与之前的调频光谱研究结果非常吻合 (Friedrichs, G.; Wagner, H. G. Z. Phys. Chem. 2001, 215, 1601)；即，在高温范围内，CH(2)与 H(2)反应中 (1)CH(2)的重要性得到了再次确认。
