Temperature Dependence of the HO2 + ClO Reaction. 2. Reaction Kinetics Using the Discharge-Flow Resonance-Fluorescence Technique
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- 作者：Kevin M. Hickson ; Leon F. Keyser ; Stanley P. Sander
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：August 23, 2007
- 年：2007
- 卷：111
- 期：33
- 页码：8126 - 8138
- 全文大小：171K
- 年卷期：v.111,no.33(August 23, 2007)
- ISSN：1520-5215
文摘
The total rate coefficient, k3, for the reaction HO2 + ClO 
f"> products has been determined over the temperaturerange of 220-336 K at a total pressure of approximately 1.5 Torr of helium using the discharge-flow resonance-fluorescence technique. Pseudo-first-order conditions were used with both ClO and HO2 as excess reagentsusing four different combinations of precursor molecules. HO2 molecules were formed by using either thetermolecular association of H atoms in an excess of O2 or via the reaction of F atoms with an excess of H2O2.ClO molecules were formed by using the reaction of Cl atoms with an excess of O3 or via the reaction of Clatoms with Cl2O. Neither HO2 nor ClO were directly observed during the course of the experiments, butthese species were converted to OH or Cl radicals, respectively, via reaction with NO prior to their observation.OH fluorescence was observed at 308 nm, whereas Cl fluorescence was observed at approximately 138 nm.Numerical simulations show that under the experimental conditions used secondary reactions did not interferewith the measurements; however, some HO2 was lost on conversion to OH for experiments in excess HO2.These results were corrected to compensate for the simulated loss. At 296 K, the rate coefficient was determinedto be (6.4 ± 1.6) × 10-12 cm3 molecule-1 s-1. The temperature dependence expressed in Arrhenius form is(1.75 ± 0.52) × 10-12 exp[(368 ± 78)/T] cm3 molecule-1 s-1. The Arrhenius expression is derived from afit weighted by the reciprocal of the measurement errors of the individual data points. The uncertainties arecited at the level of two standard deviations and contain contributions from statistical errors from the dataanalysis in addition to estimates of the systematic experimental errors and possible errors from the appliedmodel correction.
f"> products has been determined over the temperaturerange of 220-336 K at a total pressure of approximately 1.5 Torr of helium using the discharge-flow resonance-fluorescence technique. Pseudo-first-order conditions were used with both ClO and HO2 as excess reagentsusing four different combinations of precursor molecules. HO2 molecules were formed by using either thetermolecular association of H atoms in an excess of O2 or via the reaction of F atoms with an excess of H2O2.ClO molecules were formed by using the reaction of Cl atoms with an excess of O3 or via the reaction of Clatoms with Cl2O. Neither HO2 nor ClO were directly observed during the course of the experiments, butthese species were converted to OH or Cl radicals, respectively, via reaction with NO prior to their observation.OH fluorescence was observed at 308 nm, whereas Cl fluorescence was observed at approximately 138 nm.Numerical simulations show that under the experimental conditions used secondary reactions did not interferewith the measurements; however, some HO2 was lost on conversion to OH for experiments in excess HO2.These results were corrected to compensate for the simulated loss. At 296 K, the rate coefficient was determinedto be (6.4 ± 1.6) × 10-12 cm3 molecule-1 s-1. The temperature dependence expressed in Arrhenius form is(1.75 ± 0.52) × 10-12 exp[(368 ± 78)/T] cm3 molecule-1 s-1. The Arrhenius expression is derived from afit weighted by the reciprocal of the measurement errors of the individual data points. The uncertainties arecited at the level of two standard deviations and contain contributions from statistical errors from the dataanalysis in addition to estimates of the systematic experimental errors and possible errors from the appliedmodel correction.