REACTIONS OF O(P-3) WITH ALKENES - H, CH2CHO, CO, AND OH CHANNELS

The H, CH2CHO, CO, and OH products of the reaction of O(P-3) atom with alkenes were studied by laser-induced fluorescence (LIF) under single -collision conditions. The average kinetic energies of the H atoms wer e 10-12 kcal/mol. The CO and OH rotational state populations were char acterized by near room temperature Boltzmann distributions. The relati ve LIF intensities of the various products provide vivid proof of the following mechanism for the reaction of O(P-3) atoms with molecules of the form R'RC=CH2, where R' and R are H or an alkyl group. The O atom attaches itself to the less substituted carbon atom forming a triplet ketocarbene. There is a barrier to the release of an H atom, and the rate of release must compete with the sate of intersystem crossing. If an H atom is not released, following the intersystem crossing an H at om migrates to the adjacent C atom forming an energized aldehyde, R'RC H-CH=O. The aldehyde dissociates unimolecularly forming the pair of ra dicals R'(.) and the substituted vinery (RCH)-R-.-CH=O or the pair R'R CH and HCO. Some of the latter have enough internal energy to dissocia te to H and CO. In a side reaction O(P-3) abstracts H atoms but only f rom allylic C-H bonds. The most remarkable observation is that chemica l reactions that do not involve the side chains such as release of H a toms or breakup of HCO depend sensitively on the length of these chain s.