The coverage dependent phase behavior of molecular films of n-alkanes (CH 3 CH nϪ2 CH 3 , denote Cn) on mercury was studied for lengths 10рnр50, using surface tensiometry and surface x-ray diffraction methods. In contrast with Langmuir films on water, where roughly surface-normal molecular orientation is invariably found, alkanes on mercury are always oriented surface-parallel, and show no long-range in-plane order at any surface pressure. At a low coverage a two-dimensional gas phase is found,

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... followed, upon increasing the coverage, by a single condensed layer (n р18), a sequence of single and double layers (19рnр20; nу26), or a sequence of single, double, and triple layers (22рnр24). The thermodynamical and structural properties of these layers, as determined from the measurements, are discussed.