The reaction of ground state lead atoms, Pb(6 3P 0), with CH 3Cl, C 2H 5Cl, n-C 3H 7Cl and SF 6 at elevated temperatures by time-resolved atomic resonance absorption spectroscopy

Abstract

The reactions of ground state lead atoms, Pb(6 3P 0), with the molecules CH 3Cl, C 2H 5Cl, n-C 3H 7Cl and SF 6 have been studied over the range of elevated temperatures 594 – 819 K by time-resolved atomic resonance absorption spectroscopy. Pb(6 3P 0) was generated by the low energy flash photolysis of PbBr 2 vapour and monitored photoelectrically in the “single-shot mode” at λ = 283.3 nm (Pb(7s( 3P° 1)) « Pb(6p 2( 3P 0))), on a time scale long by comparison with that for the relaxation of Pb(6p 2( 3P 1,2)). The decay profiles of the ground state lead atoms were characterized in the presence of the halides RX, leading to the determination of the absolute second-order rate constants k RX for removal and the following Arrhenius parameters ( k RX = A exp(— E/RT)): RX A (X10 −11cm 3 molecule −1 −1) E (kJ mol −1) CH 3Cl 4.5 74.2 ± 3.8 C 2H 5Cl 8.0 76.2 ± 8.4 n-C 3H 7Cl 7.2 65.8 ± 3.5 SF 6 74 93.0 ± 7.3 (errors, 1σ). These data are considered in the context of the relevant thermochemistry and compared with the analogous results for the reactions of lead atoms with alkyl bromides that we have reported previously. These two groups of measurements constitute the first body of Arrhenius data for halogen atom abstraction from alkyl halides by lead atoms, fundamental parameters long established for a wide range of other metal atoms.