Thermally Initiated Formation of Criegee Intermediate CH₂OO in the Oxidation of Ethane

Criegee intermediates (CIs) play an important role in atmospheric chemistry as a transient source of the OH radical through their formation by the ozonolysis of unsaturated organic compounds. Here, we report thermally initiated formation of the smallest CI (CH₂OO) in the oxidation of ethane (CH₃CH₃) that may be relevant to combustion and flames. The SiO₂/SiC oxidation microreactor is heated to 1800 K and has a short residence time of ∼100 μs. The CH₂OO we observe is likely formed in a lower-temperature region near the microreactor's exit. Plausible mechanisms for CH₂OO formation and retention under these conditions mediated by methylperoxy (CH₃OO) radicals are discussed. Pure rotational spectra of CH₂OO and other intermediates (HO₂, CH₃CHO, CH₂CHOH, <i>c-</i>CH₂OCH₂, CH₃CH₂CHO, CH₃OOH, and HCOOH) are detected with a chirped-pulse Fourier transform millimeter-wave spectrometer operating in the frequency range of 60-90 GHz. Detection occurs in a molecular beam, where the species are supersonically cooled to 5 K.