THE STRUCTURE OF A BROMOMETHANE MONOLAYER ADSORBED ON GRAPHITE

The structure of a bromomethane monolayer adsorbed on graphite is determined by a combination of X-ray and neutron diffraction. The experimentally determined unit cell is incommensurate with the graphite and is rectangular with lattice parameters a = 3.035 nm and b = 0.555 nm. There are eight molecules in the unit cell, arranged to give four zig-zag chains of molecules. Alternation of adjacent pairs of chains leads to no overall dipole moment for the layer. All eight molecules lie approximately flat on the surface, and the layer resembles the (010) plane of the bulk crystal. The melting point of the layer is determined to lie in the range 110-120 K.