Kinetic studies of Bi(6 4S [formula omitted]) by time-resolved atomic resonance fluorescence I: Reactions with C 2H 2 (+He), N 2O and fluorescence quenching of Bi(7 4P [formula omitted

Abstract

We present a kinetic study of ground state atomic bismuth Bi(6 4S 3 2 ) generated by pulsed irradiation of Bi(CH 3) 3 in the presence of various gases and monitored with time-resolved atomic resonance fluorescence in the “single-shot” mode at λ = 306.8 nm (Bi(7 4P 1 2 ) → Bi(6 4S 1 2 ) + hv) following optical excitation. The third-order reaction Bi + C 2H 2 + He is studied in detail, including the effects of diffusion. The resulting third-order rate constant ( k 3 = (1.9 ± 0.3) × 10 −33 cm 6 molecule −2 s −1 (300 K)) is compared with previous data, in particular those from time-resolved resonance absorption measurements. The absolute second-order rate constant for the reaction between Bi(6 4S 3 2 ) and N 2O is also characterized ( k 2 = (2.1 ± 0.4) × 10 −16 cm 3 molecule −1 s −1 (300 K)) and compared with previous upper limits reported for this reaction. Finally, the technique is applied to the study of fluorescence quenching of Bi(7 4P 1 2 ) for which we report the following quenching cross sections σ 2 (Å 2) (errors, about 25%): N 2, 3.8; NO, 169; O 2, 570; N 2O, 164; CF 4, 12; C 2H 2, 97. These data are compared, where possible, with measurements of quenching cross sections derived from Stern—Volmer analyses on integrated plate intensities resulting from atomic emission following flash photolysis. The results from the two fundamentally different techniques are found to be in reasonable accord.