Hydrodynamics and molecular motion: A phenomenological approach

A series of phenomenological macro-micro correlations is developed for single and multi-particle correlation functions descriptive of molecular rototranslation. The relation between hydrodynamic and molecular theories of molecular motion may then be investigated in the Markov limit. It is emphasised that a Mori continued fraction for non-Markov statistics and molecular motion on the single particle level is inconsistent with the unmodified viscoelastic approach exemplified by Bixon and Zwanzig. The analytical autocorrelation function must be related to a multimolecule correlation function via a macro-micro relation before comparison with the hydrodynamic theories is fruitful.