Charge-quadrupole

Curves plotted for AH° conv. hyd. and ionic radii given in Tables 5 and 6, and in col. 2 of Table 1 are shown in Fig. 4 for both alkali cations and halide anions. The uncertainty in the thermochemical data is taken as 0.5 kcal and the uncertainty in ionic radii is based on deviations from additivity of r0 values. From these curves A(AH° conv. hyd.) can be estimated and in Fig. 5 these values halved are plotted against (R- -a) 3. This curve becomes linear for large (i a)-3 values and this supports the use of the model based on charge-quadrupole interactions and assumptions concerning differences in kinetic contributions to the internal energy (39). 

As we stated at the beginning of this section, most of the work in this area has focused upon the study of molecular orientation at the liquid-vapor interface and how this is affected by details of the intermolecular forces. Thompson and Gubbins have carried out molecular dynamics simulations of the vapor-liquid interface for homonuclear 12-6 diatomic molecules and for such molecules with point-charge quadrupoles. They find that in the case of the nonpolar molecules, there is a tendency for molecules in the liquid to align perpendicular to the surface and those in the vapor to align parallel to the surface. The addition of a quadrupole to the 12-6 diatomic " reverses this effect. A study of the vapor-liquid interface for an interaction site model of -octance leads to similar conclusions as for the nonpolar diatomic. These effects are reproduced qualitatively by all the theoretical approximations, with the exception of the influence of the quadrupole, which can only be predicted at first order within the context of the perturbation theory based upon division of the Mayer function Eq. (3.5.2). 

Bounds PJ, Munn RW (1981) Polarization energy of a localized charge in a molecular-crystal. 2. Charge-quadrupole energy. Chem Phys 59 41... 

M possesses a nonzero dipole moment, g. [If M has no dipole moment but a nonzero quadrupole moment, Q, then the asymptotic form of the potential is a charge-quadrupole interaction, V(r) -Q/r. ] The M -l-e potential well in Figure 4(a) is much shallower than that for M" " -l-e, consistent with the observation that IPs for neutral atoms and molecules are large compared to EAs. As such, the anion typically possesses few (if any) bound Rydberg states. ... 

The first energy component UoiDi results from the dipole-dipole interactions between molecules of the same kind i. The second one Ua-other stems from the interactions of the dipole i with all other sources of electrostatic coupling, the non-dipolar multipoles of the species i (charges, quadrupoles, etc.) as well as all multipoles (including dipoles) of the other species. 

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