Studies of transient intermediates

Ketene was flash photolysed at wavelengths greater than 160 nm. The photolysis lamp was of a four electrode pair design, with Marx - Bank circuitry, operating at 1000 J with a 1/e decay time of -4%. The major new result is the observation of "singlet products", ethane and methane, at limiting high inert gas pressures, in mixtures containing low pressures of hydrogen. Various schemes are suggested to explain this result; the most satisfactory one implicates CH2 (1B1) in the reaction system. At low pressures, acetylene was formed in larger quantities than could be explained by any kinetic scheme involving CH2. Its presence is attributed to heating effects or to alternative decomposition modes of CH2CO at low pressure. The rate constants for reaction of CH2 (3B1) + CH3, and of CH2 (1A1) with H2, CH4 and CH2CO are discussed. The rate constant for reaction of CH2 (1B1 with H2 is estimated on the assumption of a fluorescent lifetime of 10-6 s. The effect of O2, NO, and CO as CH2 scavengers is also discussed. RRKM calculations for several radical - radical reactions are presented. The reactions - of the various electronic states of methylene and the photolysis of ketene are discussed in terms of electronic symmetry.