Knowledge Bank

The reaction of ozone with olefins is one of the major reaction pathways responsible for the formation of photochemical smog in the troposphere over major urban areas. Because of this, much work has gone into the elucidation of the reaction mechanism. From this previous work the reaction sequence is thought to proceed as out lined below: [FIGURE] In all of the previous experimental work the primary ozonide (A), and the Criegee intermediate (B) have never been observed in solution or gas phase experiments although they are both thought to be key intermediates in the overall reaction scheme. Their existence has only been inferred from secondary chemical evidence involving chemical trapping and end product analysis. Now, for the first time, the primary ozonide (A) has been observed in the prototypical reaction of ozone with ethylene, the smallest olefin. The rotational spectra of six isotopic species have been observed at $-100\circ C$ using a specially designed low temperature absorption cell. The free molecule in the gas phase exhibits an envelope type of structure with the central oxygen forming a $50\circ$ out of plane ``flap'' of the five membered heavy atom ring. Details of the structural determination and the dipole moment analysis will be presented.