The reaction kinetics of amino radicals with sulfur dioxide

Application of the laser photolysis-laser-induced fluorescence method to the reaction NH₂+SO₂ in argon bath gas yields pressure-dependent, third-order kinetics which may be summarized as k = (1.49 ± 0.15) × 10^-31 (T/298 K)^-0.83cm⁶ molecule^-2 s^-1 over 292-555K, where the uncertainty is the 95% confidence interval and includes possible systematic errors. The quenching of vibrationally excited NH₂ is consistent with a high-pressure limit for NH₂+SO₂ of (1.62 ± 0.25) × 10^-11cm³ molecule^-1 s^-1 over the temperature range 295-505K, where again the 95% confidence interval is shown. Ab initio analysis yields a H₂N-SO₂ dissociation enthalpy of 73.5 kJ mol^-1, and comparison with RRKM theory and the exponential down model for energy transfer yields <ΔE>_down = 350 cm^-1 for Ar at room temperature.