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

Abstract

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 2 OO) in the oxidation of ethane (CH 3 CH 3 ) that may be relevant to combustion and flames. The SiO 2 /SiC oxidation microreactor is heated to 1800 K and has a short residence time of ∼100 μs. The CH 2 OO we observe is likely formed in a lower-temperature region near the microreactor's exit. Plausible mechanisms for CH 2 OO formation and retention under these conditions mediated by methylperoxy (CH 3 OO) radicals are discussed. Pure rotational spectra of CH 2 OO and other intermediates (HO 2 , CH 3 CHO, CH 2 CHOH, c-CH 2 OCH 2 , CH 3 CH 2 CHO, CH 3 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.