Thermally Initiated Formation of Criegee Intermediate CH 2 OO 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 (CH OO) in the oxidation of ethane (CH CH ) that may be relevant to combustion and flames. The SiO /SiC oxidation microreactor is heated to 1800 K and has a short residence time of ∼100 μs. The CH OO we observe is likely formed in a lower-temperature region near the microreactor's exit. Plausible mechanisms for CH OO formation and retention under these conditions mediated by methylperoxy (CH OO) radicals are discussed. Pure rotational spectra of CH OO and other intermediates (HO , CH CHO, CH CHOH, CH OCH , CH CH CHO, CH OOH, 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.