Structural study of a chloroform film adsorbed on graphite

The structural characterization of a chloroform (CHCl3) film adsorbed on graphite was performed by means of X-ray and neutron diffraction between 40 and 227 K. Results are consistent with those of a previous thermodynamic characterization and can be related to difficulties in the adsorbed film nucleation. The first layer melts at 166 K. At 227 K, the CHCl3 bilayer spectrum is that of a liquid, in agreement with the 225 K melting temperature determined from the isotherm measurements. The diffraction profiles of solid adsorbed CHCl3 are representative of a mixture of two structures on a microscopic scale. One of them is hexagonal with a 5.91 Angstrom parameter, and appears to be the most stable, the second is a square unit cell with a 5.77 Angstrom parameter. (C) 1998 Elsevier Science B.V.