Temperature-Dependent Kinetics Study of the Reactions of OH with C2H5I, n-C3H7I, and iso-C3H7I


  • Zhang Shaoliang
  • Strekowski Rafal S.
  • Monod Anne
  • Bosland Loic
  • Zetzsch Cornelius

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Flash photolysis (FP) coupled with resonance fluorescence (RE) was used to measure the absolute rate coefficients for the reactions of OH(X-2 Pi) radicals with C2H5I (k(1)), n-C3H7I (k(2)), and iso-C3H7I (k(3)) at temperatures between 297 and 372 K in 188 Torr of He; this represents the first temperature-dependent kinetics studies for the title reactions. The experiments involved time-resolved RE detection of the OH (A(2)Sigma(+) -> X-2 Pi transition at lambda = 308 nm) radicals following FP of H2O/C2H5I/He, H2O/n-C3H7I/He, and H2O/iso-C3H7I/He mixtures. The OH(X-2 Pi) radicals were produced by FP of H2O in vacuum-UV at wavelengths lambda > 120 nm. Decays of OH radicals in the presence of C2H5I, n-C3H7I, and iso-C3H7I were observed to be exponential, and the decay rates were found to be linearly dependent on the C2H5I, n-C3H7I, and iso-C3H7I concentrations. The results are described by the following Arrhenius expressions (units of cm(3) molecule(-1) s(-1)): k(1)(297-372 K) = (5.55 +/- 3.20) x 10(-12) exp[-(830 +/- 90) K/T], k(2)(300-370 K) = (1.65 +/- 0.90) x 10(-11) exp[-(780 +/- 90) K/T] and k(3)(299-369 K) = (7.58 +/- 3.70) x 10(-12) exp[-(530 +/- 80) K/T]. Reported errors in E/R and in the pre-exponential factors are 2 sigma random errors, returned by the weighted (by 1/sigma(2)) least-squares fits to the kinetic data. The implications of the reported kinetic results for understanding both atmospheric and nuclear safety interests of C2H5I, n-C3H7I, and iso-C3H7I are discussed.

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