Production and Decay of PbI(g) from the 308-Nm Photodissociation of PbI2(g)

An extensive investigation of the production and decay of ground-state PbI(g) molecules from the 308-nm XeCl excimer laser photodissociation of PbI2(g) is reported. The laser fluence dependence of the PbI yield along with energetic considerations suggests that PbI is produced by a one-photon process. PbI decay profiles as a function of argon pressure, PbI2 pressure, laser fluence, and cell temperature were determined. These results suggest that PbI and the other likely photodissociation product, I, decay back to PbI2 by a complex mechanism involving an exothermic preequilibrium. We propose a complex mechanism that includes the PbI2 catalyzed recombination of PbI and I and the dimerization of PbI molecules. The proposed mechanism also takes into account the presence of Pb formed from the two-photon photodissociation of PbI2 and is capable of reproducing the observed PbI(g) and Pb(g) decay profiles under most conditions studied when: reasonable values of rate constants for the various elementary steps are used.