Polarizability interaction-induced

The dielectric constant e of a gas sample depends on the total dipole moment induced in response to an applied electric field. The dipole moment is the vector sum of the partially oriented permanent dipoles pt which individual molecules i may possess, plus the field-induced dipoles a, E arising from the polarizability a of the molecules i, plus all interaction-induced dipoles fiik, plus the field-induced dipoles which arise from the interaction-induced polarizability ptk [93]. The dielectric constant e depends, therefore, on the density g of the gas, according to... 

Potential energy surfaces of weakly bound dimers and trimers are the key quantities needed to compute transition frequencies in the high resolution spectra, (differential and integral) scattering cross sections or rate coefficients describing collisional processes between the molecules, or some thermodynamic properties needed to derive equations of state for condensed phases. However, some other quantities governed by weak intermolecular forces are needed to describe intensities in the spectra or, more generally, infrared and Raman spectra of unbound (collisional complexes) of two molecules, and dielectric and refractive properties of condensed phases. These are the interaction-induced (or collision-induced) dipole moments and polarizabilities. 

In view of Eqs. (1-237) and (1-238), the components of the interaction-induced dipole moment and polarizability can written as,... 

In Ref. (316) the SAPT approach has been applied to compute the interaction-induced polarizability of the helium diatom. Before discussing the Raman spectra obtained from the SAPT collision-induced polarizabilities, let us discuss the importance of various physical contributions to the parallel and perpendicular components of the collision-induced polarizability tensor. 

This is analyzed in Tables 1-13 and 1-14 where the computed values of A.azz and Aaxx in terms of SAPT contributions at various interatomic distances are reported. The largest contributions to the components of the interaction-induced polarizability are given by the first-order terms. Except for the smallest interatomic distance (R = 3 bohr), the sum Aa pol +Aa exch, i = z or x, reproduces more than 88% of the total... 

Table 1-13. SAPT contributions (in 10 3 a.u.) to the parallel component of the interaction-induced polarizability of He2 as function of the interatomic distance R (in bohr)...

Moszynski R, Heijmen TGA, van der Avoird A (1995) Second dielectric virial coefficient of helium gas quantum-statistical calculations from an ab initio interaction-induced polarizability. Chem Phys Lett 247 440- 146... 

Hattig C, Larsen H, Olsen J, J0rgensen P, Koch H, Fernandez B, Rizzo A (1999) The effect of intermolecular interactions on the electric properties of helium and argon. I. Ab initio calculation of the interaction induced polarizability and hyperpolarizability in He2 and Ar2. J Chem Phys 111 10099-10107... 

Collision-induced light scattering is the name for the Raman spectroscopy that arises from the interaction-induced variations of the polarizability of a sample. For a description of the scope of CILS, we consider briefly two somewhat extreme cases, a tenuous gas and a liquid. 

In general, the polarizability is a tensor whose invariants, trace and anisotropy, give rise to polarized and fully depolarized light scattering, respectively. Collision-induced light scattering is caused by the excess polarizability of a collisional pair (or a larger complex of atoms or molecules) that arises from the intermolecular interactions. In Section I.l, we are concerned with the definition, measurement, and computation of interaction-induced polarizabilities and their invariants. 

F. Barocchi, M. Zoppi, U. Bafile, and R. Magli. The pair polarizability anisotropies of Kr and Xe from depolarized interaction induced light scattering spectra. Chem. Phys. Lett., 97 135-138 (1983). 

Atom-Atom Interactions. - The methods applied, usually to interactions in the inert gases, are a natural extension of diatomic molecule calculations. From the interaction potentials observable quantities, especially the virial coefficients can be calculated. Maroulis et al.31 have applied the ab initio finite field method to calculate the interaction polarizability of two xenon atoms. A sequence of new basis sets for Xe, especially designed for interaction studies have been employed. It has been verified that values obtained from a standard DFT method are qualitatively correct in describing the interaction polarizability curves. Haskopoulos et al.32 have applied similar methods to calculate the interaction polarizability of the Kr-Xe pair. The second virial coefficients of neon gas have been computed by Hattig et al.,33 using an accurate CCSD(T) potential for the Ne-Ne van der Waals potential and interaction-induced electric dipole polarizabilities and hyperpolarizabilities also obtained by CCSD calculations. The refractivity, electric-field induced SHG coefficients and the virial coefficients were evaluated. The authors claim that the results are expected to be more reliable than current experimental data. 

These findings provided a consistent picture of the investigated systems and helped in separating different interaction-induced polarizability mechanisms. Furthermore, the analysis pointed out the important role of the local structure symmetry around the anion to the variation of the isotropic scattering intensity with composition and temperature. 

MULTIPOLAR POLARIZABILITIES FROM INTERACTION-INDUCED RAMAN SCATTERING... 

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