Location and motion of aromatic guest molecules within Na X and Na Y zeolites have been probed with xenon. Xenon perturbs the photophysical properties of the excited singlet state:of aromatic guest molecules through the external heavy atom effect. Naphthalene, phenanthrene, and pyrene have been used as guests, and they are nonuniformly distributed within zeolites, as indicated by their multiexponential decay of excited singlet states. Of the many locations in which the guest molecules are speculated to be present, only one has photophysical properties which are influenced by the presence of xenon. Diffusion coefficients estimated by the photophysical method presented here compare favorably with the numbers obtained by other conventional methods.