Eskola Arkke J, Wojcik-Pastuszka Dorota, Ratajczak Emil, Timonen Raimo S
Laboratory of Physical Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), FIN-00014, Finland.
Phys Chem Chem Phys. 2006 Mar 28;8(12):1416-24. doi: 10.1039/b516291b. Epub 2006 Feb 13.
The kinetics of the reactions of CH2Br and CH2I radicals with O2 have been studied in direct measurements using a tubular flow reactor coupled to a photoionization mass spectrometer. The radicals have been homogeneously generated by pulsed laser photolysis of appropriate precursors at 193 or 248 nm. Decays of radical concentrations have been monitored in time-resolved measurements to obtain the reaction rate coefficients under pseudo-first-order conditions with the amount of O2 being in large excess over radical concentrations. No buffer gas density dependence was observed for the CH2I + O2 reaction in the range 0.2-15 x 10(17) cm(-3) of He at 298 K. In this same density range the CH2Br + O2 reaction was obtained to be in the third-body and fall-off area. Measured bimolecular rate coefficient of the CH2I + O2 reaction is found to depend on temperature as k(CH2I + O2)=(1.39 +/- 0.01)x 10(-12)(T/300 K)(-1.55 +/- 0.06) cm3 s(-1)(220-450 K). Obtained primary products of this reaction are I atom and IO radical and the yield of I-atom is significant. The rate coefficient and temperature dependence of the CH2Br + O2 reaction in the third-body region is k(CH2Br + O2+ He)=(1.2 +/- 0.2)x 10(-30)(T/300 K)(-4.8 +/- 0.3) cm6 s(-1)(241-363 K), which was obtained by fitting the complete data set simultaneously to a Troe expression with the F(cent) value of 0.4. Estimated overall uncertainties in the measured reaction rate coefficients are about +/-25%.
利用与光离子化质谱仪联用的管式流动反应器，通过直接测量研究了CH2Br和CH2I自由基与O2的反应动力学。在193或248nm波长下，通过对合适前驱体进行脉冲激光光解，均相产生自由基。在时间分辨测量中监测自由基浓度的衰减，以获得在O2量大大超过自由基浓度的准一级条件下的反应速率系数。在298K时，He的密度范围为0.2 - 15×10(17) cm(-3)，未观察到CH2I + O2反应对缓冲气体密度的依赖性。在相同密度范围内，CH2Br + O2反应处于三体和过渡区。测得CH2I + O2反应的双分子速率系数与温度的关系为k(CH2I + O2)=(1.39 ± 0.01)×10(-12)(T/300 K)(-1.55 ± 0.06) cm3 s(-1)(220 - 450 K)。该反应的主要产物是I原子和IO自由基，I原子的产率很高。CH2Br + O2反应在三体区域的速率系数和温度依赖性为k(CH2Br + O2+ He)=(1.2 ± 0.2)×10(-30)(T/300 K)(-4.8 ± 0.3) cm6 s(-1)(241 - 363 K)，这是通过将完整数据集同时拟合到F(cent)值为0.4的Troe表达式得到的。测得的反应速率系数的估计总不确定度约为±25%。
