The collisional behaviour of ground state bismuth atoms, Bi(6 4S 0[formula omitted], with alkyl bromides studied by time- resolved atomic resonance fluorescence at λ = 306.77 nm (Bi(7 4P [formula omitted])) following pulsed irradiation: kinetics, radiation trapping and fluorescence quenching of Bi(7 4P [formula omitted

Abstract

The kinetic study of ground state bismuth atoms, Bi(6 4S 0 3 2 ), has been investigated by time-resolved atomic resonance fluorescence at λ = 306.77 nm (Bi(7 4P 1 2 )-Bi(6 4S 0 3 2 ) in the “single-shot” mode following pulsed irradiation. Bi(6 4S 0 3 2 ) was generated by the flash photolysis of Bi(CH 3) 3 in the presence of excess helium buffer gas and monitored as a function of time with various added bromine-containing molecules as reactants. Absolute second-order rate constants k R Br (cm 3 molecule −1 s −1) ( T = 300 K; errors, 2σ) are reported for the removal of Bi(6 4S 0 3 2 ) by the following molecules: Br 2, (5.3 ± 1.8) × 10 −13; CH 2Br 2, (9.0 ± 1.3) × 10 −15; CH 3Br, (1.8 ± 0.4) × 10 −15; C 2H 5Br, (4.1 ± 0.7) × 10 −15; n-C 3H 7Br, (1.2 ± 0.1) × 10 −14. These results are compared with analogous rate data for the reaction of ground state lead atoms, Pb(6 3P 0). We also present detailed calculations of radiation trapping using various models including the diffusion theory of radiation involving a characteristic mean free path of an emitted photon and a more generalized transport theory for the (Bi(7 4P 1 2 )-Bi(6 4S 0 3 2 )) transition, including the effect of nuclear hyperfine interaction. Consideration is given in the present paper to radiation trapping calculations for atomic densities where the simplifying approximations resulting from the use of “low equivalent opacities” break down. The results of these calculations are presented for various models which lead to relations describing the variation in the effective mean radiative lifetime with atomic density and the functional relationship between fluorescence intensity and particle density.