THE ATOMIC ORIGINS OF THE QUADRUPOLE AND 2ND MOMENTS IN THE SERIES CO2, OCS, AND CS2

The theory of atoms in molecules is used to investigate the change in the molecular second and quadrupole moments in the series carbon dioxide, carbonyl sulphide, and carbon disulphide. Simple electronegativity arguments would predict that the quadrupole moments of all three molecules should be negative, but experimental observations have found that the quadrupole moment decreases throughout the series with that for CS2 being positive. The trend in the second and quadrupole moments is shown to result from the decreased charge transfer away from carbon as oxygen is replaced by sulphur through the series. The study is extended to include carbon monoxide, carbon sulphide, formaldehyde, and thioformaldehyde and the same physical characteristics are shown to determine the moments in these systems.