Diffusion theory and picosecond atom recombination

Abstract

We attempt to describe our picosecond iodine recombination data using simple diffusion theory. The physical picture is simple. Recombination of iodine atoms is the result of the diffusive motion of two iodine atoms, with such parameters as viscosity and temperature together with the diffusion theory governing the motion. The difference between most tests of diffusion theory and the present one is the extremely short time scale of our experimental data. We are thus close to, if not already in, the regime where the solvent structure is noncontinuous. In this regime the fundamental hypothesis of diffusion theory is invalid and one would not expect diffusion theory to be valid. We compare several different formulations of the diffusion equation solutions using different boundary conditions. The comparisons of each of these treatments with the experimental data fails. A discussion of the implications of this result, as well as some suggestions for improving the applicability of diffusion theory is presented.