The intermolecular potential of methane: a neutron diffraction study on low-density CD4

Neutron diffraction on low-density systems offers the possibility of a direct probing of the intermolecular forces. This method, used in the last few years for monatomic systems like rare gases, is applied here to the case of gaseous CD4 at low densities on the 180 K isotherm. The intermolecular scattering has been analysed in order to extract C(q), i.e. the Fourier transform of the direct correlation function. The zero-density limit of C(q), which depends on the (spherical average of the) pair potential only, is compared to the same quantity obtained from effective intermolecular pair potentials found in the literature.