Nuclear quadrupole resonance and intermolecular interactions: temperature and pressure effects in Group V trichlorides

Nuclear quadrupole resonance frequencies for the metal and chlorine atoms in AsCl3 and SbCl3 have been measured as functions of temperature and pressure. These data are analysed to obtain the isothermal volume dependences and the isochoric temperature dependences of the field gradient parameters. Existing knowledge of the Group V trichlorides shows that the strength of intermolecular bonding increases in the order AsCl3 < SbCl3 < BiCl3, and this trend is reflected in the relative importance of volume effects in determining the nqr frequencies in these solids. A simple theory of the pressure dependences of nqr frequencies in molecular crystals is proposed, which accounts for all data presently available. The pressure coefficient contains static and dynamic contributions which are of opposite signs; the static contribution is negative and becomes numerically larger as the strength of intermolecular bonding increases.