The Use And Limits Of The CIS Technique For The Measurements Of Hyperpolarizabilities : the H2-Rg case

Date du colloque&nbsp;: 10/2010</p

Moments of hyper-Rayleigh spectra of selected rare gas mixtures

In this work we have analyzed spectral moments characterizing properties of the collisionally hyper-Rayleigh scattered light. This is a supplementary study undertaken in order to complete the series of our previously published papers on the collisional hyper-Rayleigh scattering spectral profiles. In order to evaluate the moments we have extended the theory so that it could embrace the hyper polarizabilities of higher rank. Using the expressions developed on the grounds of the theoretical principles and applying appropriate computational methods with ab initio hyperpolarizability values as an input, we have obtained desirable moment values for three diatomic noble gas systems: HeNe, HeAr, and NeAr, at several temperature points. The semiclassical and the quantum treatments have been taken into account, and the moments were calculated both from the sum rule method as well as from the spectral profiles. The results were compared and discussed

Hyper-Rayleigh spectral intensities of gaseous Kr–Xe mixture

Binary collision-induced hyper-Rayleigh s CIHR d spectra of Kr–Xe gaseous system are computed quantum mechanically and classically within the frequency range up to 380 cm−1. The intensities are expressed in absolute units. The details of the theory developed for the CIHR spectra are given and the properties of the profiles as well as the depolarization ratio frequency dependence are discussed. The contributions to the spectra related to the vector b10(r) and the septor b30(r) components of the hyperpolarizability tensor are evaluated

Collision-induced hyper-Rayleigh spectrum of H2–Ar gas mixture

The collision-induced hyper-Rayleigh (CIHR) spectra of the gaseous H 2 – Ar mixture are discussed in the binary regime on the basis of our ab initio computed H 2 – Ar collision-induced (CI) first dipole hyperpolarizability tensor Δ β ( R ) . A method for the computation of the spherical, rotationally adapted components Δ β λ L ( s , K ) ( R ) of Δ β ( R ) needed for spectroscopic line shape analysis is proposed. Both the vector and the septor parts of the H 2 – Ar CIHR spectrum are evaluated at room ( T = 295 K ) temperature. The spectra are calculated assuming the full quantum computations based on the Schrödinger equation of the relative translational motion of H 2 – Ar as well as semiclassical methods (classical trajectory approach and Birnbaum–Cohen model translational profiles). The H 2 – Ar pair CIHR septor spectrum has been found stronger than the vector one

Collision-induced hyperpolarizability and hyper-Rayleigh spectra in the He–Ar heterodiatom

The ab initio interatomic distance dependent collision induced dipole moment, polarizability and the vector b1 (R) and an irreducible 3rd rank tensor b3 (R) components of the first hyperpolarizability tensor b of He–Ar pair are obtained. The hyperpolarizability data are applied in order to calculate the collision induced He–Ar hyper-Rayleigh spectra both quantum-mechanically and semiclassically for the frequency shifts up to 1200 cm-1. Computations were carried out for two temperature values – T = 295 K and T = 95 K. Spectral features of both vector and the irreducible 3rd rank tensor parts of CIHR spectra are analyzed. The frequency dependent behavior of the HR depolarization ratio is discussed

Second Harmonic Elastic Light Scattering by Gases Composed of Centrosymmetric Molecules. The Case of H2‐Ar.

A numerical and theoretical study of nonlinear collisional electrical and/or optical properties of near van der Waals weakly bound complexes is presented. The molecular systems considered are composed of a linear nonpolar molecule ( H 2 taken as an example) and a spherical atomic entity (Ar)—a supermolecule of symmetry of one step lower than that considered before. The basic stage of the procedure developed consists of computational quantum chemistry efforts of determining values of the first hyperpolarizability tensor for several intermolecular configuration arrangements. Subsequent theoretical discussion includes these quantities within a routine developed in order to produce symmetry adapted (SA) components of the hyperpolarizability tensor, which are finally used so that the spectral distributions of the collision‐induced hyper‐Rayleigh (CIHR) light scattering could be determined. Translational parts of these functions have served as an assessment tool to judge about the role played by a particular SA contribution in the overall tensorial property. In particular, the convergence of the series expansion of the hyperpolarizability dependence on intermolecular distances has been investigated. Three computational methods based on quantum and semiclassical approach have been compared

Collision-induced hyper-Rayleigh light scattering in gaseous dihydrogen-neon mixtures

Cartesian components of the collision-induced (CI) hyperpolarizability Δβ tensor are computed for the linear, T-shaped, and 45∘ configurations of the H2-Ne pair in the intermolecular range 3 to 14 bohr. Symmetry-adapted components Δβ(K)λ L(R) of the vector (K=1) part, as well as the septor (K=3) part, of the H2-Ne CI hyperpolarizability are calculated starting from the ab initio Cartesian hyperpolarizability tensor values transformed into their spherical counterparts. By applying these quantities, the vector together with the septor collision-induced hyper-Rayleigh (CIHR) spectra for the H2-Ne binary gas mixture are determined in the frequency range from −1250 to 2500 cm−1. The profiles are partially employed as a benchmarking device to estimate the importance of the short intermolecular distance part of the Δβ(R) dependence. The depolarization ratio of the CIHR spectra in the whole frequency range is also calculated. The nature of the CIHR signal and the feasibility of the related experiments are discussed and analyzed

Collisional ab initio hyperpolarizabilities in computing hyper-Rayleigh spectra of noble gas heterodiatomics

We review some recent studies on the theoretical and computational aspects of collision-induced nonlinear properties and phenomena, such as: the first hyperpolarizability of inert gas heteroatomic pairs (He-Ne, He-Ar, N-Ar and Kr-Xe) and spectral properties of hyper-Rayleigh scattered light in such systems. The hyperpolarizability data obtained by means of a variety of methods of quantum chemistry were applied to calculate spectral HR profiles. Computations are performed both quantum-mechanically and classically for two temperature values T=95 K and T:295 K. Resulting tensorial properties and spectra are presented and discussed