The structure of carbon dioxide around naphthalene investigated using H/D substitution in neutron diffraction

The technique of hydrogen/deuterium substitution in neutron diffraction has been used to investigate the intermolecular structure of carbon dioxide saturated with naphthalene at supercritical pressure. The experiment was performed at P = 206 bar and T = 302 K, corresponding to a dilute concentration of approximately 1 C10H8 molecule to 110 CO2 molecules. Particular attention has been paid to the local structural environment of the hydrogen atoms through the extraction of the first-order neutron difference function. The neutron data show that eight nearest-neighbor CO2 molecules form a well-defined ring around the hydrogen atoms on the naphthalene molecule. Moreover, the CO2 molecules appear to be oriented perpendicular to the plane of the naphthalene molecule at a distance of r(H-CO2) = 3.3 Angstrom.