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 (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, c-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.