KINETIC-STUDY OF NEUTRAL LEAD CLUSTER REACTIONS

Kinetic studies of the reactions of neutral lead clusters with NO2, NO and O2 were performed at 300 K. Reaction with NO2 is rapid, with the observed second-order rate constants for most clusters being between 0.2 and 5 x 10(-11) cm3/s. There is a general trend of increasing rate with cluster size, although a few clusters display unusually high or low rates compared to ones of neighboring size. The reactions with NO are considerably slower by factors ranging from about 5 to 10. Reaction products are observed by laser ionization at 193 and 222 nm in conjunction with time-of-flight mass spectrometry. At lower fluence, the association products Pbx(NO2)+ and Pbx(NO2)2+ are observed in the case of reactions with NO2. At higher laser fluence, Pb+ and PbxOx-1+ dominate the mass spectra of Pb(x) reactions with NO2, showing that the products fragment to more stable oxides. No reaction with oxygen was observed for any cluster, setting upper limits on the rates of 5 x 10(-14) cm3/s.