We have obtained the monolayer structure diffraction patterns from several iodoalkanes adsorbed on graphite, of interest in the study of non-covalent bonding. However, it is clear that three possible structures are consistent with the xray data as it is dominated by the heavy iodine atoms and cannot identify the positions of the rest of the molecules. Here we request neutron time to distinguish these three possibilities, given the sensitivity of neutrons to all the atoms present in the layer.