An Experimental and Master Equation Study of the Kinetics of OH/D + SO₂: The Limiting High Pressure Rate Coefficients

The kinetics of the reaction OH/OD + SO₂ have been studied using a laser flash photolysis / laser induced fluorescence technique. Evidence for two-photon photolysis of SO₂ at 248 nm is presented and quantified, and which appears to have been evident to some extent in most previous photolysis studies, potentially leading to values for the rate coefficient, k₁, that are too large. The kinetics of the reaction OH(v=0) + SO₂ (T = 295 K, p = 25 – 300 Torr) were measured under conditions where SO₂ photolysis was taken into account. These results, together with literature data, were modelled using a master equation analysis. This analysis highlighted problems with the literature data: the rate coefficients derived from flash photolysis data were generally too high and from the flow tube data too low. Our best estimate of the high-pressure limiting rate coefficient, k₁∞ was obtained from selected data and gives a value of (7.8 ± 2.2) × 10¯¹³ cm³ molecules¯¹, which is lower than that recommended in the literature. A parameterized form ofk₁([N₂],T) is provided. The OD(v=0) + SO₂ (T = 295 K, p = 25 – 300 Torr) data are reported for the first time and master equation analysis reinforces our assignment of k₁∞.