Production and Decay of Ground-State Pb(g) from the 308-nm Photodissociation of PbI2(g)

Article abstract of DOI:10.1021/j100177a044

An extensive investigation of the production and decay of ground-state lead atoms from the 308-nm XeCl excimer laser photodissociation of PbI2(g) is reported.The laser fluence dependences of Pb(g) and PbI(g) yields along with energetic considerations suggest that Pb(g) is produced by a two-photon process and PbI(g) is produced by a one-photon process.Pb decay profiles as a function of argon pressure, PbI2(g) number density, laser fluence, and cell temperature were determined.The rates of Pb decay were found to be approximately second order in Pb.The second-order rate-constants were found to increase with PbI2(g) number density, to not change with argon pressure, and to decrease with increasing laser fluence and cell temperature.These results are consistent with a complex mechanism that can be described as the PbI2(g)-catalyzed recombinations of Pb and PbI with I involving an exothermic preequilibrium, I + PbI2= PbI3, with ΔH ca. -22 +/- 6 kcal/mol.The proposed mechanism is capable of reproducing the observed Pb(g) decay profiles under all conditions studied when reasonably large values of rate coefficients for the various elementary steps are used.