相对速率法测量氯原子与几种酮类物质的反应速率常数

在(298±2) K和一个大气压条件下,采用相对速率法研究了一系列酮类物质与氯原子的反应动力学.使用丙醛和乙苯作为参比物,光解三氯乙酰氯作为氯原子产生源,测得2-己酮与氯原子的反应速率常数为(1.80±0.42)×10~(-10) cm~3·molecule~(-1)·s~(-1),与已有文献报道值非常符合,验证了实验方法和所选参比物的可靠性.首次测得了(298±2) K和一个大气压条件下2-庚酮和2-辛酮与氯原子反应的速率常数,分别为(2.54±0.62)×10~(-10)和(2.12±0.63)×10~(-10) cm~3·molecule~(-1)·s~(-1).与其母体烷烃的反应速率对比发现,酮类物质中羰基的存在使得其反应速率都比其母体烷烃变慢.利用所测的速率常数和氯原子的浓度信息估算这些酮类物质在大气中的平均寿命,结果显示,在海洋边界层或沿海地区等氯原子浓度较高的地区,这些物质与氯原子反应的大气化学寿命都在小时量级,完全可以与OH自由基的反应相竞争,是这些物质在大气中的重要降解途径.另外,在内陆污染地区或工业聚集区,氯原子的反应及其对二次污染物生成的贡献同样不能忽视.

Rate constants for gas-phase reactions of Cl atoms with a series of ketones by relative rate method

Reaction kinetics of several ketones with chlorine atoms was studied using the relative rate method at (298±2) K and atmospheric pressure. The reaction rate constant of 2-hexanone with chlorine atoms was measured to be (1.80±0.42)×10^-10 cm³·molecule^-1·s^-1 using propionaldehyde and ethylbenzene as reference compounds, which is in good agreement with the reported values in the literature. And the rate constants for reactions of 2-heptanone and 2-octanone with chlorine atoms were measured for the first time, which were (2.54±0.62)×10^-10 and (2.12±0.63)×10^-10 cm³·molecule^-1·s^-1, respectively. Compared with reaction rate constants of their parent alkanes with chlorine atoms, it was found that the presence of carbonyl group in these ketones makes their rate constants smaller than those of their parent alkanes. The average lifetimes of these ketones in the atmosphere have also been estimated using the measured rate constants. The results showed that the reaction with chlorine atoms could be an important degradation pathway for these ketones, which can compete with their reactions with OH radicals, especially in areas with high concentration of chlorine atoms such as marine boundary layer and coastal areas. In addition, in some inland polluted areas or industrial agglomeration areas where the concentration of chlorine atom is also relatively high, the reaction of chlorine atoms and their contribution to the formation of secondary pollutants could also not be ignored.