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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Absolute rate coefficient determination and reaction mechanism investigation for the reaction of Cl atoms with CH2I2 and the oxidation mechanism of CH2I radicals
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Absolute rate coefficient determination and reaction mechanism investigation for the reaction of Cl atoms with CH2I2 and the oxidation mechanism of CH2I radicals

机译：Cl原子与CH2I2的反应及CH2I自由基的氧化机理的绝对速率系数确定及反应机理研究

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摘要

The gas-phase reaction of atomic chlorine with diiodomethane was studied over the temperature range 273363 K with the very low-pressure reactor (VLPR) technique. The reaction takes place in a Knudsen reactor at pressures below 3 mTorr, where the steady-state concentration of both reactants and stable products is continuously measured by electron-impact mass spectrometry. The absolute rate coefficient as a function of temperature was given by k = (4.70+/-0.65) x 10(-11) exp[-(241+/-33)/T] cm(3) molecule(-1)s(-1), in the lowpressure regime. The quoted uncertainties are given at a 95% level of confidence (2 sigma) and include systematic errors. The reaction occur's via two pathways: the abstraction of a hydrogen atom leading to HCl and the abstraction of an iodine atom leading to ICl. The HCl yield was measured to be ca. 55+/-10%. The results suggest that the reaction proceeds via the intermediate CH2I2-Cl adduct formation, with a I-Cl bond strength of 51.9+/-15 kJ mol(-1), calculated at the B3P86/aug-cc-pVTZ-PP level of theory. Furthermore, the oxidation reactions of CHI2 and CH2I radicals were studied by introducing an excess of molecular oxygen in the Knudsen reactor. HCHO and HCOOH were the primary oxidation products indicating that the reactions with O-2 proceed via the intermediate peroxy radical formation and the subsequent elimination of either IO radical or I atom. HCHO and HCOOH were also detected by FT-IR, as the reaction products of photolytically generated CH2I radicals with O-2 in a static cell, which supports the proposed oxidation mechanism. Since the photolysis of CH2I2 is about 3 orders of magnitude faster than its reactive loss by Cl atoms, the title reaction does not constitute an important tropospheric sink for CH2I2.
机译：使用超低压反应器（VLPR）技术研究了在273363 K的温度范围内原子氯与二碘甲烷的气相反应。该反应在Knudsen反应器中在低于3 mTorr的压力下进行，在该反应器中，反应物和稳定产物的稳态浓度均通过电子碰撞质谱法连续测量。绝对速率系数与温度的关系为k =（4.70 +/- 0.65）x 10（-11）exp [-（241 +/- 33）/ T] cm（3）分子（-1）s （-1），处于低压状态。所引用的不确定性以95％的置信度（2 sigma）给出，包括系统误差。该反应通过两种途径发生：夺取HCl的氢原子和夺取ICl的碘原子。测得的HCl收率为约3。 55 +/- 10％。结果表明反应是通过中间CH2I2-Cl加合物形成而进行的，I-Cl键强度为51.9 +/- 15 kJ mol（-1），在B3P86 / aug-cc-pVTZ-PP水平下计算理论。此外，通过在Knudsen反应器中引入过量的分子氧，研究了CHI2和CH2I自由基的氧化反应。 HCHO和HCOOH是主要的氧化产物，表明与O-2的反应是通过中间过氧自由基的形成以及随后的IO自由基或I原子的消除而进行的。 FT-IR还检测到HCHO和HCOOH，这是在静态电池中光解生成的CH2I自由基与O-2的反应产物，这支持了所提出的氧化机理。由于CH2I2的光解作用比其Cl原子的反应损失快3个数量级，因此标题反应不会对CH2I2构成重要的对流层汇。

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