Criegee intermediates, which are carbonyl oxides produced when ozone reacts with unsaturated hydrocarbons, play an important role in the formation of OH and organic acids in the atmosphere, but they have eluded direct detection until recently. Reactions that involve Criegee intermediates are not understood fully because data based on their direct observation are limited. We used transient infrared absorption spectroscopy to probe directly the decay kinetics of formaldehyde oxide (CH2OO) and found that it reacts with itself extremely rapidly. This fast self-reaction is a result of its zwitterionic character. According to our quantum-chemical calculations, a cyclic dimeric intermediate that has the terminal O atom of one CH2OO bonded to the C atom of the other CH2OO is formed with large exothermicity before further decomposition to 2H2COÂ +Â O2(1Îg). We suggest that the inclusion of this previously overlooked rapid reaction in models may affect the interpretation of previous laboratory experiments that involve Criegee intermediates. Criegee intermediates play an important role in atmospheric chemistry but their direct study has proved difficult. Transient infrared absorption spectroscopy has now been used to probe the decay kinetics of the Criegee intermediate CH2OO directly, revealing that its self-reaction is extremely rapid. This may have important consequences for the interpretation of previous laboratory experiments.
克里基中间物是
臭氧与不饱和碳氢化合物反应时产生的羰基氧化物,在大气中形成 OH 和有机酸的过程中发挥着重要作用,但直到最近才被直接检测到。由于基于直接观测的数据有限,人们对涉及克里基中间体的反应还不完全了解。我们利用瞬态红外吸收光谱直接探测了氧化
甲醛(CH2OO)的衰变动力学,发现它与自身的反应速度极快。这种快速的自我反应是其具有齐聚离子特性的结果。根据我们的量子
化学计算,在进一步分解为 2H2COÂ +Â O2(1δg)之前,会形成一个环状二聚中间体,其中一个 CH2OO 的末端 O 原子与另一个 CH2OO 的 C 原子成键,放热很大。我们认为,在模型中加入这种以前被忽视的快速反应可能会影响对以前涉及克里基中间体的实验室实验的解释。克里基中间产物在大气
化学中发挥着重要作用,但对它们的直接研究却很困难。现在,我们利用瞬态红外吸收光谱直接探测了克里基中间体 CH2OO 的衰变动力学,发现它的自我反应非常迅速。这可能会对解释以前的实验室实验产生重要影响。