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Abstract

The oscillatory NO+CO reaction on Pt(100) has been investigated in the 10⁻⁶ mbar range using photoemission electron microscopy (PEEM) as a spatially resolving method. The existence ranges for kinetic oscillations have been mapped out in (p_CO,T)‐parameter space with fixed p_NO=4×10⁻⁶ mbar. Kinetic oscillations occur within a partial pressure range of 0.8<p _NO/p _CO <1.9. In the lower lying of two temperature windows for oscillatory reaction behavior, the oscillations proceed unsynchronized on a 1×1 substrate without exhibiting macroscopic rate variations. Instead, one observes spatiotemporal pattern formation which has been studied in detail. These patterns are dominated by periodic wave trains, which become unstable at lower temperatures, giving rise to spiral waves and irregularly shaped reaction fronts. With decreasing temperature, the front velocity increases, while simultaneously the spatial periodicity of the wave trains becomes larger. In agreement with theoretical predictions by a three‐variable model, the local oscillations terminate at the upper T boundary via a Hopf bifurcation and at the lower T boundary via a bifurcation of the saddle‐loop type.