The structural second virial coefficient, the intermolecular potential for nitrogen and the magnetic scattering for the oxygen molecule

Measurements of the slow neutron scattering cross-section at 0·5 Å for nitrogen gas and oxygen gas at room temperature and low density are reported. The results are interpreted in terms of a new quantity, the structural second virial coefficient, B 2(Q, T), where B 2(O, T) is the conventional second virial coefficient. It is shown that for nitrogen the observed function, or the ‘difference’ cross-section, corresponds quite well to that calculated for an isotropic Lennard-Jones potential and less well for recently proposed anisotropic potentials. The method is promising for the determination of interaction potentials for molecules. For oxygen the contribution to the scattering due to the molecular paramagnetism is evaluated. The total cross-section is as predicted theoretically but the differential cross-section is significantly different.