The reaction of IO with CH3SCH3: products and temperature dependent rate coefficients by laser induced fluorescence

Abstract

The technique of pulsed laser photolysis was coupled to laser induced fluorescence detection of iodine oxide (IO) to measure rate coefficients, k₁(T), for the title reaction IO + CH₃SCH₃ → products (R1). A value of k₁(298 K) = (1.44 ± 0.15) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ was obtained, independent of bath gas pressure (50 < P_{(N2 or air)}/Torr < 300). The expression k₁(T) = (3.2 ± 1.4) × 10⁻¹³exp{(−925 ± 136)/T)} adequately described the data over the range of temperatures (256 < T/K < 341) covered. Uncertainties (2σ) in the 298 K rate coefficient and the pre-exponential factor include an estimate of systematic error. The conventional Arrhenius behaviour of k₁(T) and the lack of pressure dependence are suggestive of an abstraction mechanism, characterised by an energy barrier of E ≈ 8 kJ mol⁻¹. The product yield for production of I-atoms was determined indirectly to be close to unity, indicating that the reaction proceeds via transfer of the O-atom from IO to CH₃SCH₃ to form CH₃S(O)CH_3. In general, the values of k₁(T) measured in this work indicate that reaction (R1) has little impact on the chemistry of the atmosphere.