Precursor effect during water vapor diffusion in a porous medium

In water vapor diffusing through a granular adsorbent layer into vacuum, water molecules overcoming an adsorption column without an appreciable delay as pulses, i.e., precursors of the main front, were detected. This effect is explained by the sluggishness of water molecule diffusion into adsorbent grains and the dependence of the adsorption capacity of molecules on their rotational states via the Stark effect in a surface electric field of an adsorbent.