Lin Hui-Yu, Huang Yu-Hsuan, Wang Xiaohong, Bowman Joel M, Nishimura Yoshifumi, Witek Henryk A, Lee Yuan-Pern
Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001, Ta-Hsueh Road, Hsinchu 30010, Taiwan.
Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA.
Nat Commun. 2015 May 11;6:7012. doi: 10.1038/ncomms8012.
The Criegee intermediates are carbonyl oxides that play critical roles in ozonolysis of alkenes in the atmosphere. So far, the mid-infrared spectrum of only the simplest Criegee intermediate CH2OO has been reported. Methyl substitution of CH2OO produces two conformers of CH3CHOO and consequently complicates the infrared spectrum. Here we report the transient infrared spectrum of syn- and anti-CH3CHOO, produced from CH3CHI + O2 in a flow reactor, using a step-scan Fourier-transform spectrometer. Guided and supported by high-level full-dimensional quantum calculations, rotational contours of the four observed bands are simulated successfully and provide definitive identification of both conformers. Furthermore, anti-CH3CHOO shows a reactivity greater than syn-CH3CHOO towards NO/NO2; at the later period of reaction, the spectrum can be simulated with only syn-CH3CHOO. Without NO/NO2, anti-CH3CHOO also decays much faster than syn-CH3CHOO. The direct infrared detection of syn- and anti-CH3CHOO should prove useful for field measurements and laboratory investigations of the Criegee mechanism.
克里奇中间体是羰基氧化物，在大气中烯烃的臭氧分解过程中起着关键作用。到目前为止，仅报道了最简单的克里奇中间体CH2OO的中红外光谱。CH2OO的甲基取代产生了CH3CHOO的两种构象体，从而使红外光谱变得复杂。在此，我们使用步进扫描傅里叶变换光谱仪，报道了在流动反应器中由CH3CHI + O2产生的顺式和反式CH3CHOO的瞬态红外光谱。在高水平的全维量子计算的指导和支持下，成功模拟了四个观测波段的转动轮廓，并明确鉴定了两种构象体。此外，反式CH3CHOO对NO/NO2的反应活性大于顺式CH3CHOO；在反应后期，光谱仅用顺式CH3CHOO即可模拟。在没有NO/NO2的情况下，反式CH3CHOO的衰变也比顺式CH3CHOO快得多。顺式和反式CH3CHOO的直接红外检测对于克里奇机理的现场测量和实验室研究应是有用的。
