Pulsed laser photolysis kinetics study of the O(3P)+ClO reaction

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Abstract
A pulsed laser photolysis technique has been employed to study the kinetics of the important stratospheric reaction O+ClO→k1Cl+O2 in N2 buffer gas over the temperature and pressure ranges 231–367 K and 25–500 Torr. 351 nm pulsed laser photolysis of Cl2/O3/N2 mixtures produced Cl atoms in excess over O3. After a delay sufficient for the reaction Cl+O3→ClO+O2 to go to completion, a small fraction of the ClO was photolyzed at 266 nm to produce O(3P). The decay of O(3P) in the presence of an excess, known concentration of ClO was then followed by time‐resolved resonance fluorescence spectroscopy. We find that k1 is independent of pressure, but that k1(T) increases with decreasing temperature. Our results suggest that the Arrhenius expression k1(T)=(1.55±0.33)×10−11 exp{(263±60)/T} cm3 molecule−1 s−1 is appropriate for modeling stratospheric chemistry. Errors in the Arrhenius expression are 2σ and represent precison only. The absolute accuracy of k1 at any temperature within the range studied is estimated to be ±20%. Our results agree with other recent measurements of k1 at 298 K but give significantly faster rate coefficients at stratospheric temperatures. A few measurements of the rate coefficient for the reaction ClO+ClO→k7products were also carried out. These measurements were necessary to assess the time dependence of [ClO].

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