Electronic polarizability studies induced dipoles

H-bonding is an important, but not the sole, interatomic interaction. Thus, total energy is usually calculated as the sum of steric, electrostatic, H-bonding and other components of interatomic interactions. A similar situation holds with QSAR studies of any property (activity) where H-bond parameters are used in combination with other descriptors. For example, five molecular descriptors are applied in the solvation equation of Kamlet-Taft-Abraham excess of molecular refraction (Rj), which models dispersion force interactions arising from the polarizability of n- and n-electrons the solute polarity/polarizability (ir ) due to solute-solvent interactions between bond dipoles and induced dipoles overall or summation H-bond acidity (2a ) overall or summation H-bond basicity (2(3 ) and McGowan volume (VJ [53] ... 

Recent work improved earlier results and considered the effects of electron correlation and vibrational averaging [278], Especially the effects of intra-atomic correlation, which were seen to be significant for rare-gas pairs, have been studied for H2-He pairs and compared with interatomic electron correlation the contributions due to intra- and interatomic correlation are of opposite sign. Localized SCF orbitals were used again to reduce the basis set superposition error. Special care was taken to assure that the supermolecular wavefunctions separate correctly for R —> oo into a product of correlated H2 wavefunctions, and a correlated as well as polarized He wavefunction. At the Cl level, all atomic and molecular properties (polarizability, quadrupole moment) were found to be in agreement with the accurate values to within 1%. Various extensions of the basis set have resulted in variations of the induced dipole moment of less than 1% [279], Table 4.5 shows the computed dipole components, px, pz, as functions of separation, R, orientation (0°, 90°, 45° relative to the internuclear axis), and three vibrational spacings r, in 10-6 a.u. of dipole strength [279]. 

In recent years Seff and co-workers (9) have extensively studied cation siting in zeolite A using single-crystal X-ray diffraction techniques. In favorable cases these workers have also been able to obtain detailed information on the interactions between cations and absorbate molecules. Two examples are shown in Fig. 4, where the adsorption complexes formed when acetylene and NO are adsorbed in Co(II)A have been resolved. In the former case it is proposed that a weak complex is formed via an induced dipole interaction with the polarizable 7i-orbitals of the acetylene molecule. For the NO complex there is good evidence for electron transfer resulting in a complex between CO(III) and NO. In both cases the organic molecules... 

Dipole-induced dipole or dipole-quadrupole interactions can give rise to weakly bound complexes of considerable importance in dynamical studies. It is therefore important that properties such as the polarizability can be accurately determined. A FCI study [6] of the polarizability of F is summarized in Table III. As in the previous examples, the SDCI treatment is not sufficiently accurate for very high quality calculations. The inclusion of an estimate of higher excitations improves the results in this case CPF is superior to the -hQ correction. In the multireference case two different approaches were used. In the first, the CASSCF included the 2p electrons and 2p and 3p orbitals in the active space, and all CASSCF CSFs were used as references for the Cl, in which the 2s and 2p electrons were correlated. Results obtained in this way are denoted MRCI in Table III. A more elaborate CASSCF calculation, with the 2s and 2p electrons and the 2s, 3s, 2p and 3j> orbitals in the active space, was also performed the use of all these CASSCF CSFs as references gives an SOCI expansion and the results are denoted SOCI in... 

Change in the dipole moment and polarizability upon electronic excitation was determined for various linear polyenes by adopting electric field-induced changes in the optical absorption spectrum [70]. Polyenes studied (Exhibit 2) were diphenylbutadiene (DPB 7), diphenylhexatriene (DPH 8), diphenyloctate-traene (DPO 9), diphenyldecapentaene (DPD 10), and all-tranj-retinal (3). Exhibit 2 describes the experimental values determined. It is proposed that (based on the results obtained) the excited state dipole moments determined on these polyene systems have a role to play in the mechanism of trans-cis photoisomerization. 

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