SYNCHRONIZATION AND SPATIOTEMPORAL SELF-ORGANIZATION IN THE NO-SUBSTRATE(CO REACTION ON PT(1OO) .2. SYNCHRONIZED OSCILLATIONS ON THE HEX)

The NOS-CO reaction exhibits sustained rate. oscillations on Pt(100) u nder conditions where the surface is mostly hex-reconstructed. These r ate oscillations have been investigated in the 10(-6) mbar range using photoemission electron microscopy as a spatially resolving method. Du ring the rate oscillations which appear in a temperature-window rangin g from 490 to 478 K, the surface reacts in a spatially homogeneous way . At the upper T-boundary of the oscillatory range, the oscillations d evelop via a Feigenbaum scenario leading from chaotic small amplitude oscillations at high T to regular period-1 oscillations at lower T. At the lower T-boundary of the oscillatory range, at T=478 K, target pat terns appear causing the collapse of the amplitude of the rate oscilla tions. As the temperature is lowered further, the parallel wave trains become increasingly irregular. Spiral waves form, and finally one obs erves only local reaction outbursts. A model for the synchronization m echanism in the rate oscillations is proposed based on the 1x1 double left right arrow hex-phase transition, while the origin of the chaotic oscillations in this reaction system is discussed in terms of a trans ition from unsynchronized to synchronized oscillations.