Ion imaging techniques are widely used in the measurement of chemical reaction dynamics in the gas phase. They allow rapid data acquisition because they enable simultaneous measurements of speed and angular distributions. The application of ion imaging to surface scattering experiments has so far been limited, but recent experiments have made great strides in measuring velocity and state resolved inelastic scattering and measurements of chemical reaction rates. Notably, we can now make measurements of reaction rates that are velocity resolved, making it possible for the first time to measure the reaction flux as a function of speed and angle. Measurements of this type on CO oxidation on Pt, COa + Oa =&gt; CO2,g on Pt surfaces provide new insights into this prototypical surface reactions. We demonstrate the measurement of CO oxidation rates at step edges and terraces on Pt(111) and Pt(332) surfaces. Reactions at terraces produce CO2 with hyperthermal speeds in narrow angular distributions, while reactions at steps produce CO with thermal speeds in broad angular distributions. This settles the long standing “two channel question” in this important reaction and reveals that all previous reports of rate parameters attributed to terrace reactions actually were dominated by reactions at steps.

Ion imaging measurements of velocity resolved reaction rates: New insights into CO oxidation on Pt

2019 Fall National Meeting

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