Polarisability dipole-quadrupole

Electron population parameters of inner monopoles were constrained to be equal for all 40 non-H atoms. Single exponentials r exp(-ar) were adopted as radial functions for the higher multipoles, with n = 2, 2, 3 respectively for dipole, quadrupole, and octopole of the species C, N and 0, and n = 4, 4, 4 for the same multipoles of the S atom. A radial scaling parameter k, to shape the outer shell monopoles, and the exponential parameter a of all non-H atomic species were also refined. H atoms were initially given scattering factors taken from the H2 molecule [15] and polarised in the direction of the atom to which they are bonded. 

These agree rather well with the experimental values listed above, suggesting that the ionic model is a good one. On the other hand, the negative Fermi contact constant can only arise through polarisation of the electron spins in a covalent bond between the two atoms. The electric dipole moment also seems to be inconsistent with a purely ionic model, yet the quadrupole coupling constant eq0Q is very close to that of the ionic molecule LiF. 

Figure 8 suggests that the second excited state should have Ag(Q = 2) symmetry if the configuration is ob, but rg(Q = 4) if it is n3. Neither of these states is accessible through the magnetic dipole transition mechanism. However when AQ = 2 the transition is allowed by the electric-quadrupole mechanism. In Fig. 6 a band near 20,405 cm-1, labelled III, in the X(y) and 7(x) polarisations... 

Absorption models of this type have also provided important information about the nature of the zeolite framework. Calculations carried out by Furuyama and co-workers on gas absorption in mordenite and ZSM-5 zeolites have shown that the charge distributions within the channels may be quite different and that the nature of the approximation used in the calculation may have some bearing upon the reliability of the results. In these calculations the interaction of molecular dipole and quadrupole moments with the electric field have been considered, in addition to the usual repulsion dispersion and polarisation terms. 

The basis sets used in the CEPA calculations were large. For example with H2HF, the F atom basis was a (10s,6p) contracted to [6s,4p] augmented with extra diffuse s and p orbitals, and 3d and 4f orbitals optimised to produce the dipole and quadrupole polarisabilities of HF. The results reported here for ArHCN did not include f orbitals in the basis set, although the sensitivity of the results to these functions is currently being examined. The CEPA potential for ArOH was calculated by Esposti and Wemer. In all cases, basis set superposition errors were accounted for. 

Fig. 3. Schematic, one-electron view of resonant magnetic scattering at the Ljjj absorption edge. The linearly polarised incident photon promotes a Ipj/j core electron into an empty state above the Fermi level. In the lanthanides there are 5d states available in the dipole approximation, and unfilled 4f states available through a quadrupole transition. Magnetic scattering results when the virtually excited electron decays, thereby filling the core hole and coherently emitting an elastically scattered photon.

Measurements and calculation of dipole moments, quadrupole moments and polarisabilities of mesogenic molecules... 

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