Reversible addition of the OH radical to p-cymene in the gas phase: kinetic analysis assuming formation of a single adduct. Part 1


  • Alarcon Paulo
  • Strekowski Rafal
  • Zetzsch Cornelius

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A flash photolysis-resonance fluorescence (FP-RF) technique was employed to study the kinetics and mechanism of the reaction of OH radicals with p-cymene at temperatures between 297 and 413 K in helium buffer gas. FP-RF experiments involved time-resolved detection of OH radicals by RF following vacuum-UV flash photolysis of H2O-p-cymene-He and H2O-He mixtures. Biexponential functions were fitted to decays of OH radicals according to reversible addition of OH radicals to p-cymene to form a single adduct. A rate constant of (15.7 +/- 1.1) x 10(-12) is obtained (in units of cm(3) s(-1)) at room temperature (298 K) for the sum of the addition and abstraction channels (k(1a) + k(1b)) according to this simplified model. The Arrhenius plot reveals the step function typical of other aromatics and can be described using the expressions: 2 x 10(-13) exp(+1300 K/T) at temperatures between 297 K and 324 K and 10(-11) exp(-250 K/T) at temperatures between 345 K and 413 K. After consideration of the abstraction channel an equilibrium constant of k(1a)/k(-1a) = 6 x 10(-26) exp(+9700 K/T) cm(3) is obtained at temperatures between 297 and 325 K and 2 x 10(-36) exp(+17 000 K/T) cm(3) at temperatures between 325 and 380 K.

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