Fingering instabilities on reaction fronts in the CO oxidation reaction on Pt(100)

Fingering instabilities arising from local perturbations to planar reaction fronts in the CO oxidation reaction on Pt(100) are presented. CO oxidation represents a heterogeneous nonlinear system with the necessary kinetic and diffusive transport properties to support the development of fingered wave fronts. External forcing was utilized to create CO wave fronts on an otherwise monostable, O-covered surface, which, upon destabilization, gave rise to fingers of adsorbed CO extending into the O adlayer ahead of the reaction front. Finger spreading and tip-splitting were observed as the finger pattern evolved towards an intrinsic wavelength, independent of the length of the reaction front, calculated to be approximately 40 mu m. Our data also show the presence of a shielding process, where at wavelengths less than twice the observed intrinsic value, additional fingers were created on the reaction front through a tip-splitting bifurcation of an existing finger. At wavelengths greater than twice the intrinsic value, additional fingers formed in the troughs between adjacent fingers, apparently unaffected by the presence of the larger surrounding fingers.