Thermally Initiated\nFormation of Criegee Intermediate\nCH<sub>2</sub>OO in the Oxidation of Ethane

Criegee intermediates (CIs) play an important role in\n atmospheric\nchemistry as a transient source of the OH radical through their formation\nby the ozonolysis of unsaturated organic compounds. Here, we report\nthermally initiated formation of the smallest CI (CH<sub>2</sub>OO)\nin the oxidation of ethane (CH<sub>3</sub>CH<sub>3</sub>) that may\nbe relevant to combustion and flames. The SiO<sub>2</sub>/SiC oxidation\nmicroreactor is heated to 1800 K and has a short residence time of\n∼100 μs. The CH<sub>2</sub>OO we observe is likely formed\nin a lower-temperature region near the microreactor’s exit.\nPlausible mechanisms for CH<sub>2</sub>OO formation and retention\nunder these conditions mediated by methylperoxy (CH<sub>3</sub>OO)\nradicals are discussed. Pure rotational spectra of CH<sub>2</sub>OO\nand other intermediates (HO<sub>2</sub>, CH<sub>3</sub>CHO, CH<sub>2</sub>CHOH, <i>c-</i>CH<sub>2</sub>OCH<sub>2</sub>, CH<sub>3</sub>CH<sub>2</sub>CHO, CH<sub>3</sub>OOH, and HCOOH) are detected\nwith a chirped-pulse Fourier transform millimeter-wave spectrometer\noperating in the frequency range of 60–90 GHz. Detection occurs\nin a molecular beam, where the species are supersonically cooled to\n5 K.