KINETIC-MODELS OF SURFACE EXPLOSIONS

The kinetics of surface 'explosions' on single-crystal surfaces has been explored by mathematical modelling of a number of possible kinetic models and examining the quality of fit to a wide range of experimental data. Second-order autocatalysis has been the previously preferred model. However, this model is inconsistent since it assumes a random distribution of adsorbates on the surface and yet islanding is known to occur in a number of 'explosive' adsorbate systems. Indeed, it is found to be necessary to assume a high local coverage (practically independent of the global coverage) near initiation sites to fit the data well. Hence, a new approach that takes into account the effect of interactions between neighbouring adsorbates is required. A circular island model is developed which incorporates the effects of asynchronous initiation and the reduced yield caused by island merging using simple assumptions. This is found to be capable of producing fits to 'explosive' desorption data as good as those obtained by the second-order model.