Knowledge Bank

The reaction of ozone with a series of naturally emitted alkenes (ethene, cis- and trans-but-2-ene, isoprene, and selected monoterpenes) has been studied. The products of the reactions have been trapped from the gas-phase into an argon matrix and have been identified by infrared spectroscopy. All of the reactions gave matrices which showed characteristic bands of the primary and secondary ozonides alongside other stable products (typically formaldehyde and acetaldehyde were the major carbonyl products). The assignment of bands to the ozonides was confirmed by experiments where the matrices were irradiated with broad-band ultraviolet-visible radiation; the highly photolabile ozonides were destroyed rapidly by such treatment. This is the first time that matrix-isolated ozonides have been generated by gas-phase reactions; in previous $studiesa$ ozonides have been generated within the solid matrix by annealing. The assignment of product bands of the ethene reaction has been confirmed by an isotopic substitution experiment utilising deuterium. For the more complex monoterpenes bands have been assigned by comparison with the simpler alkenes. These results are of considerable interest in the field of atmospheric chemistry where ozone-alkene reactions are known to contribute to pollution of the troposphere.