Kinetic studies of the ground state lead atoms Pb(6 3P 0) generated by pulsed irradiation and monitored by time-resolved fluorescence at λ = 405.78 nm (Pb(7 3P 1) → Pb(6 3P 2)) following optical excitation at λ = 283.31 nm (Pb(7 3P 1) ← Pb(6 3P 0))

Abstract

We describe the first kinetic study of ground state lead atoms by time-resolved atomic fluorescence spectroscopy. Pb(6 3P 0) was generated by the pulsed irradiation of Pb(CH 3) 4 in the presence of helium using a high intensity magnetically pinched Garton-Wheaton light source. The transient atom was monitored in the time-resolved mode by off-resonance (direct-line) fluorescence at λ = 405.78 nm (Pb(7 3P 1) → Pb(6 3P 2)) following resonance excitation at λ = 283.31 nm (Pb(7 3P 1 ← Pb(6 3P 0)). The construction of an intense resonance source for atomic lead involved further application of the microwave-powered cavity originally developed in the Philips Laboratories at Eindhoven which was constructed in these laboratories and used earlier for the kinetic study of atomic bismuth. The photoelectric signals were recorded in the “single-shot” mode using pretrigger photomultiplier gating and were analysed in digital form by computer. The kinetic study included an investigation of the diffusion of Pb(6 3P 0) in helium together with the third-order reactions with oxygen and NO (plus helium) for which we report the following absolute rate constants (300 K): k(Pb + O 2 + He) = (2.5 ± 0.2) × 10 −32 cm 6 molecules −2 s −1 k(Pb + NO + He) = (9 ± 3) × 10 −31 cm 6 molecules −2 s −1 These are compared with previous estimates reported from time-resolved atomic resonance absorption measurements on Pb(6 3P 0). Finally, we report fluorescence quenching cross sections for Pb(7 3P 1) of σ NO 2 = 38 ± 3 Å 2 and σ O 2 2 = 12 ± 8 Å 2, which are in agreement with data reported earlier from atomic emission measurements on flames.