Roy E. McClean

Temperature-dependent studies of the reaction of W(a 5DJ, a 7S3) with O2

The gas-phase reactivities of W(a 5DJ, a 7S3) with O2 in the temperature range 298–573 K are reported. Tungsten atoms were produced by the photodissociation of W(CO)6 and detected by laser-induced fluorescence. The disappearance rate constant of the s1d5 a 7S3 state is of the order of the gas kinetic rate constant. The removal rate constants for the s2d4 a 5DJ states are J dependent. The a 5DJ states are not as reactive as the s1d5 a 7S3 state and are found to be temperature dependent. The disappearance rates of all states in the presence of O2 are found to be pressure independent with buffer gas. Physical quenching rate constants for the excited states in the presence of Ar, He, N2 and SF6 are also reported. Results are discussed in terms of the different electron configurations of the states.

Production and decay of ground-state gaseous lead from the 308-nm photodissociation of gaseous lead diiodide

An extensive investigation of the production and decay of ground-state lead atoms from the 308-nm XeCl excimer laser photodissociation of PbI[sub 2](g) is reported. The laser fluence dependences of the 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, PbI[sub 2](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 PbI[sub 2](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 PbI[sub 2](g)-catalyzed recombinations of Pb and PbI with I involving an exothermic preequilibrium, I + PbI[sub 2] = PbI[sub 3], with [Delta]H [approx] [minus]22 [plus minus] 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.