INTERACTION OF BALLISTIC PARTICLES WITH IRREGULAR PORE WALLS, KNUDSENDIFFUSION, AND CATALYTIC EFFICIENCY

The statistical behavior of ballistic trajectories in irregular two-di mensional systems is studied numerically. The geometrical irregularity is modeled by specific prefractal shapes. Many statistical distributi ons arising from these trajectories are found to obey power laws of th e Levy type with an exponent of order -2. This is the case for the pro bability distribution of the collision numbers, collision frequencies, trajectory lengths, and free paths. The results are applied to severa l physical systems in which these statistics govern the physical prope rties. The global absorption of light by irregular, partially absorbin g surfaces is found to be weakly dependent on the geometrical irregula rity. In contrast, the mean interaction of a gas with an irregular sur face increases strongly with the irregularity of the surface. Catalyti c efficiency is also found to increase strongly with irregularity. How ever, surface irregularity has only weak effects on the macroscopic Kn udsen diffusion. These conclusions are not modified when the partially random character of the interaction on the pare wall is taken into ac count.