Temperature dependence of the oxide ion/ozone reaction in the gas phase

Rate coefficient and branching fraction data were determined for the gas phase reaction of O− + O3 over the temperature range 123-500 K using the temperature variable selected ion flow tube technique. The reaction rate coefficient is large and relatively insensitive to temperature; reaction takes place on every collision. In contrast, the product distributions are sensitive to temperature. Charge transfer is the major reactive pathway (≥67%) at all temperatures, and its importance increases with increasing temperature. Atom transfer, forming O2− + O2, constitutes approximately 33% of the products at 123 K. The temperature dependence of the branching fraction explains an apparent discrepancy between product data from room temperature flow tube experiments and low energy beam experiments. A reaction mechanism is proposed to qualitatively explain the product branching fraction temperature dependence.