Laboratory of Physical Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), FIN-00014 Finland.
J Phys Chem A. 2009 Mar 5;113(9):1753-9. doi: 10.1021/jp809193w.
The gas-phase kinetics of three ethyl radical reactions with NO(2) have been studied in direct measurements using a laser photolysis/photoionization mass spectrometer (LP-PIMS) coupled to a temperature controlled tubular flow reactor. Reactions were studied under pseudo-first-order conditions with NO(2) always in large excess over initial radical concentrations. All the measured rate coefficients exhibit a negative temperature dependence, which becomes stronger as the chlorine substitution in the alpha-carbon of the ethyl radical increases. No pressure dependence of the rate coefficients was observed within the experimental range covered (0.5-6 Torr). The obtained results can be expressed conveniently as follows: k(CH(3)CH(2) + NO(2)) = (4.33 +/- 0.13) x 10(-11) (T/300 K)(-0.34 +/- 0.22) cm(3) s(-1) (221-365 K), k(CH(3)CHCl + NO(2)) = (2.38 +/- 0.10) x 10(-11) (T/300 K)(-1.27 +/- 0.26) cm(3) s(-1) (221-363 K), and k(CH(3)CCl(2) + NO(2)) = (1.01 +/- 0.02) x 10(-11) (T/300 K)(-1.65 +/- 0.19) cm(3) s(-1) (248-363 K), where the given error limits are the 1sigma statistical uncertainties of the plots of log k against log(T/300 K). Overall uncertainties in the measured rate coefficients were estimated to be +/-20%. The observed reactivity toward NO(2) decreases with increasing chlorine substitution at the radical site as was expected with respect to our previous measurements of chlorine containing methyl radical reactions with NO(2). A potential reason for the observed reactivity differences is briefly discussed, and a possible reaction mechanism is presented.
三种乙基自由基与二氧化氮的气相反应动力学已通过激光光解/光电离质谱仪（LP-PIMS）与温度控制管式流动反应器直接测量进行了研究。在准一级条件下研究了反应，二氧化氮始终过量于初始自由基浓度。所有测量的速率系数均表现出负温度依赖性，随着乙基自由基α-碳上氯取代的增加而增强。在所覆盖的实验范围内（0.5-6 托），未观察到速率系数的压力依赖性。获得的结果可以方便地表示如下：k(CH(3)CH(2) + NO(2)) = (4.33 +/- 0.13) x 10(-11) (T/300 K)(-0.34 +/- 0.22) cm(3) s(-1) (221-365 K)，k(CH(3)CHCl + NO(2)) = (2.38 +/- 0.10) x 10(-11) (T/300 K)(-1.27 +/- 0.26) cm(3) s(-1) (221-363 K)，和 k(CH(3)CCl(2) + NO(2)) = (1.01 +/- 0.02) x 10(-11) (T/300 K)(-1.65 +/- 0.19) cm(3) s(-1) (248-363 K)，其中给出的误差限制是 log k 与 log(T/300 K) 图的 1sigma 统计不确定性。测量的速率系数的总体不确定度估计为 +/-20%。正如我们之前对含氯甲基自由基与二氧化氮反应的测量所预期的那样，自由基位点上氯取代的增加导致对二氧化氮的反应性降低。简要讨论了观察到的反应性差异的可能原因，并提出了可能的反应机制。
