Transition to chaos in an oscillating surface reaction

The isothermal catalytic oxidation of CO on a Pt(110) surface in a gradientless flow reactor at low pressure (<10^-4 Torr) exhibits under properly chosen conditions (P_co, Po₂, T) sustained temporal oscillations of the reaction rate as monitored through the variation of the work function Δφ. Experimental data are presented in which by small, stepwise changes of the CO partial pressure the time series undergo a transition from simple periodic via a sequence of period doublings to aperiodic behavior as characteristic for the Feigenbaum route to chaos. Analysis of the data was performed by evaluating the power spectra, autocorrelation functions, three-dimensional attractors, correlation integrals, the Lyapunov exponents, as well as the lower limit for the Kolmogorov entropy. These results allow clear identification of deterministic chaos (including its embedding dimension n = 5 which agrees with the minimum number of variables determining the physical properties of the investigated system) as well as its distinction from periodic or random (noise) behavior.