Lattice model for translational and rotational motions based on generalised diffusion equations: I. General formalism

A simple lattice model based on generalised diffusion equations and Gaussia n statistics, aimed at describing diffusive translational and rotational mo tions, is presented. It is shown that it allows the generation of correlati on functions relevant to spectroscopic techniques that are very similar to those experimentally observed in a large variety of complex systems. For so me ranges of values of the model parameters, these functions, which can be expressed in closed mathematical forms, can be approximately. represented l y the sum of two exponentials or by "stretched" exponentials.