Rate constant measurements for the reaction of HO2 with O3 from 200 to 300 K using a turbulent flow reactor

Scott C. Herndon, Peter W. Villalta, David D. Nelson, John T. Jayne, Mark S. Zahniser

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The rate constant for the reaction of HO2 with O3 was measured using a turbulent flow reactor with tunable diode laser absorption detection of HO2. Two separate methods were used to determine k1 from the pseudo-first-order decay of HO2 in excess O3. The isotopic labeling method used H18O2 in excess 16O3 to avoid reformation of the reactant. The OH scavenger method used trifluorochloroethylene to remove the OH product and prevent re-formation of HO2. The turbulent flow reactor allowed measurements at temperatures between 297 and 197 K at total pressures from 80 to 175 Torr, spanning a wide range of stratospheric conditions. The temperature-dependent rate constant is given by the three-term expression k1(T) = {(103 ± 57) exp[-(1323 ± 160)77] + 0.88} × 10-15 cm3 molecule-1 s-1, reflecting its non-Arrhenius behavior at low temperatures. These results demonstrate that the catalytic destruction of lower stratospheric O3 by HOx radicals (OH and HO2) may proceed faster than current models predict. The rate constant at 295 K is (2.0 ± 0.2) × 10-15 cm3 molecule-1 s-1.

Original languageEnglish (US)
Pages (from-to)1583-1591
Number of pages9
JournalJournal of Physical Chemistry A
Issue number9
StatePublished - Mar 8 2001


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