Determination of absolute rate data for the reaction of atomic sodium, Na(3 2S1/2), with CF3Cl, CF2Cl2, CFCl3, CF3Br and SF6 as a function of temperature by time-resolved atomic resonance-absorption spectroscopy at λ= 589 nm [Na(3 2PJ)â†� Na(3 2S1/2)]

Abstract

We present a kinetic study of the reactions of ground-state sodium atoms with the molecules CF₃Cl, CF₂Cl₂, CFCl₃, CF₃Br and SF₆ over the temperature range 644–918 K. Na(3 ²S_1/2) was generated by the low-energy pulsed irradiation of NaI vapour above NaI solid at elevated temperatures in the presence of added reactants and monitored photoelectrically in the ‘single-shot mode’ by time-resolved atomic resonance absorption of the D lines at λ= 589 nm [Na(3 ²P_J–3 ²S_1/2)], unresolved to ensure adherence to the Beer–Lambert law. The photoelectric signals were amplified without distortion, captured, digitised and stored in a transient recorder interfaced to a microcomputer for kinetic analysis. Absolute second-order rate constants for the reaction of sodium with these gases were determined at five temperatures within the overall temperature range, leading to the followin Arrhenius parameters [k=A exp (–E/RT), errors 1 σ]: [graphic omitted].

These results, including data for CF₄, for which only an upper limit to the rate constant is presented, are compared with analogous results derived previously using sodium diffusion-flame measurements at single temperatures.