The Monte Carlo simulation method is used to study orientational ordering in monolayer films of diatomic molecules on the (100) plane of face centered cubic crystal. Systems of admolecules with different elongation are studied and their orientational and positional ordering discussed. It is shown that in the case of small elongations the adsorbed monolayer orders into a simple (1 x 1) structure. When the elongation of adsorbed molecules increases, the film orders into more complex structures. In such cases, the adsorbate lattice decomposes into four interpenetrating sublattices.