Octupolar contribution

In order to quantify the dipolar to octupolar conbibution to the NLO response, two spherical components of j3 related to the dipolar and octupolar molecular anisotropy are employed. They represent the dipolar and octupolar contributions to the NLO response of the molecules. The expressions which define them are, respectively ... 

In addition to the magnetic dipole and electric quadrupole an octupolar contribution (w) of the hyperfine interaction at the lanthanide site has also to be considered. The transition freqeuncy is described by (McCausland and Mackenzie 1980)... 

Though in the HRS expression, an isotropic average is made for molecule s all the (i tensor components, indicating that the HRS is sensitive to all such contributions. But for octupolar molecules, only <(i > tensor contributes to the total (5. 

For a purely octupolar molecule, the orientational contribution to yEnsH should be 0, so the measured value should correspond as a whole to the electronic contribution. Therefore, the information on the tensor is almost entirely expressed in the jShrs- For the unsubstituted SubPc 2, the jShrs at A = 1.06/rrn are in the range measured for donor subphthalocyanines 6, 8 and 9 at A = 1.46jU,m. The /3hrs value measured for the unsubstituted SubNc 15 is about a factor 2 smaller. 

Ray reviews some recent developments concerning the design of novel materials with large NLO effects. He considers a series of organic salts and various organometallic derivatives where it was found that metal-to-ligand charge-transfer has a dominant contribution to the second-order NLO response. He also discusses the first hyperpolarizability of several retinal derivatives, ionic octupolar molecules and zwitterionic derivativatives. Solvent effects on NLO properties are also reviewed. 

Over recent years there has been a steady growth of interest in vibrational effects in the context of ab initio calculations of linear and non-linear molecular response functions. It has been realized that in some cases vibrational may rival electronic contributions to the parameters controlling non-linear optical responses. This is particularly likely where the molecule is of higher symmetry (quadrupolar or octupolar rather than dipolar), and for lower frequency effects where there is little pre-resonant enhancement of the electronic contribution. The main features of the theoretical methodology for the calculation of vibrational response functions were established several years ago and the fundamental papers were reviewed in the previous volume. Recent developments have been the introduction of field induced co-ordinates, improved integration techniques and the first relativistic studies. ... 

---