Ozonolysis of isoprene to produce Criegee intermediates such as methyl vinyl ketone oxide (MVKO), C₂H₃C(CH₃)OO, is an important process in atmospheric chemistry. MVKO was recently produced and identified in laboratories after photolysis of a gaseous mixture of 1,3-diiodo-but-2-ene, (CH₂I)HC═C(CH₃)I, and O₂, but the mechanism of its formation remains unexplored. We synthesized pure (Z)- and (E)-1,3-diiodo-but-2-ene and measured their distinct IR spectra. Upon irradiation at 280 nm of (Z)- and (E)-1,3-diiodo-but-2-ene in solid p-H₂ at 3.3 K, the fission of the terminal C—I bond yields (Z)- and (E)-3-iodo-but-2-en-1-yl [^•C₂H₃C(CH₃)I] radicals, respectively. These radicals were characterized with infrared absorption lines at 2962.4, 1423.8, 1265.3, 1120.9/1127.0, 921.4/922.3, and 792.5/791.7 cm^–1, and 16 additional weaker lines for (Z)-^•C₂H₃C(CH₃)I and 1405.2, 1208.2, 1106.0/1103.9, 934.2/933.4, and 785.1/784.9 cm^–1 and five additional weaker ones for (E)-^•C₂H₃C(CH₃)I. The assignments were derived according to behavior on secondary photolysis and comparison of the vibrational wavenumbers and the IR intensities of observed lines with those calculated with the B2PLYP-D3/aug-cc-pVTZ-pp method. These observations confirmed that only the terminal I atom, not the central one, was photodissociated at 280 nm and, in solid p-H₂, the excess energy after photodissociation induced no change in conformation. These new spectra of ^•C₂H₃C(CH₃)I radicals can provide valuable information for the understanding of the mechanism of formation of Criegee intermediate MVKO from the source reaction of photolysis of (CH₂I)HC═C(CH₃)I in O₂ in the laboratory.

中文翻译：

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（Z）-和（E）-•C2H3C（CH3）I自由基的红外光谱，是由（Z）-和（E）-（CH2I）HC═C（CH3）I在固体对氢中光解离而产生的。

异戊二烯的臭氧分解以产生Criegee中间体，例如甲基乙烯基酮氧化物（MVKO），C ₂ H ₃ C（CH ₃）OO是大气化学中的重要过程。MVKO是在将1，3-二碘丁-2-烯，（CH ₂ I）HC═C（CH ₃）I和O ₂的气态混合物光解后在实验室中生产和鉴定的，但其机理是形成仍未探索。我们合成了纯的（Z）-和（E）-1,3-二碘代丁-2-烯，并测量了它们独特的IR光谱。固体p -H _2中的（Z）-和（E）-1,3-二碘代丁-2-烯在280 nm处辐照在3.3 K时，末端C-I键的裂变产生（Z）-和（E）-3-碘-丁-2-烯-1-基[ ^• C ₂ H ₃ C（CH ₃）I]基团， 分别。这些自由基的特征是在2962.4、1423.8、1265.3、1120.9 / 1127.0、921.4 / 922.3和792.5 / 791.7 cm ^–1处具有红外吸收谱线，并且对于（Z）- ^• C ₂ H ₃ C（CH ₃）I和1405.2、1208.2、1106.0 / 1103.9、934.2 / 933.4和785.1 / 784.9 cm ^–1，以及（E）- ^• C _2的另外五个较弱的H ₃ C（CH ₃）I。根据二次光解的行为以及将观察到的谱线的振动波数和IR强度与用B2PLYP-D3 / aug-cc-pVTZ-pp方法计算得到的谱线进行比较，得出分配。这些观察结果证实，仅末端I原子而不是中心原子在280nm处光解离，并且在固体p- H _2中，光解后的过量能量不引起构象变化。这些新的光谱^• ç ₂ ħ ₃ C（CH ₃I自由基可为实验室中O ₂中（CH ₂ I）HC═C（CH ₃）I的光解反应中的克里基中间体MVKO的形成机理提供有价值的信息。