J.-L. Godet

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 Deltabeta(R). A method for the computation of the spherical, rotationally adapted components Deltabeta(lambdaL) ((s,K))(R) of Deltabeta(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 Schrodinger 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.

Binary rototranslational hyper-Rayleigh spectra of H2–He gas mixture

The collision-induced rototranslational hyper-Rayleigh spectra of gaseous H(2)-He mixture are computed and discussed in the binary regime. As the input data we use our ab initio computed H(2)-He collision-induced first dipole hyperpolarizability tensor Deltabeta(R). Both the vector and the septor part of the H(2)-He hyper-Rayleigh spectra are evaluated at room temperature (T=295 K). The spectra are calculated assuming the full quantum computations based on the Schrödinger equation of the relative translational motion in the isotropic H(2)-He potential as well as using semiclassical methods.

Hyper-Rayleigh spectral intensities of gaseous Kr-Xe mixture.

Binary collision-induced hyper-Rayleigh (CIHR) 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 depolarized scattering by CF4 in a Raman vibrational band

Collision-induced scattering data have been recorded at room temperature for gaseous tetrafluoromethane in a frequency vicinity of the Raman vibrational line ν1=908 cm−1. For the first time, corresponding binary depolarized intensities have been measured in absolute units for frequency shifts up to 110 cm−1 from the band center. Comparison with theoretical semiclassical intensities computed from dipole-induced dipole and dipole-multipole light scattering mechanisms leads to an evaluation of the first derivative of the dipole-quadrupole polarizability tensor A′. This result is in good agreement with recent ab initio quantum-chemistry calculations of the CF4 multipolar polarizabilities.

depolarized light scattering by CF 4

Tetrafluoromethane gas depolarized scattering has been recorded at 294·5 K and 20·3 amagat in the frequency range 2-340 cm−1. Two-body depolarized scattered intensities have been measured in absolute units up to 150 cm−1. The theoretical intensities taking into account multipolar polarizabilities and several hyperpolarizability contributions have been calculated. From comparison with experiment, the independent components of the dipole-quadrupole and the dipole-octopole polarizability tensors have been estimated and checked with recent ab initio theoretical values.

HIGHER ORDER COEFFICIENT MEASUREMENTS IN NONLINEAR ABSORPTION PROCESS

Intensity-dependent two-photon absorption in chalcogenide glasses has been experimentally observed. Analytical solution of the basic differential equation giving the intensity at the output of the sample is difficult to obtain in this case. A quasi-analytical solution is provided. Second and third-order nonlinear coefficients are deduced from experimental data using Runge–Kutta numerical integration on data obtained via Z-scan technique. Results of the measured higher-order nonlinear coefficients are given. Comparison of these results with those obtained by various approximate analytical solutions of the differential equation is made.

Collision-induced hyper-Rayleigh spectrum of octahedral molecules: The case of SF6

A theoretical expression giving the collision-induced hyper-Rayleigh (CI HR) spectrum due to pairs of centrosymmetric molecules of octahedral symmetry has been derived. The dipole2-quadrupole hyperpolarizability light scattering mechanism of collision-induced hyperpolarizability ΔβLM is discussed in detail and proposed to explain the CI HR spectrum. Numerically we have applied our analytical formulas to binary CI HR spectrum of sulfur-hexafluoride. We have normalized our SF6 CI HR spectrum to the monomer HR spectrum of CCl4. The spectral contribution due to second hyperpolarizability-permanent hexadecapole HR light scattering mechanism has been estimated and showed to be negligible.

Collection Angle Dependence of the Depolarization Ratio in Light-Scattering Experiments

We have calculated, in a typical scattering experiment, the exact value of the intensity scattered by a sample for any value of the collection angle of the scattered beam and for different beam polarizations.

Isotropic collision induced light scattering spectra from gaseous SF6

The experimental binary isotropic collision-induced light scattering spectrum of the gaseous sulfur hexafluoride is measured in absolute units in the 30–210 cm−1 frequency range. The contribution of dipole–multipole mechanisms is computed in a semi-classical way. From comparison with experiment, the independent component E of the dipole–octopole polarizability tensor is estimated. This evaluation is compared to a recent theoretical ab initio calculation.

Isotropic collision-induced scattering by CF4 in a Raman vibrational band

Light-scattering intensities and depolarization ratio data have been recorded at room temperature for gaseous tetrafluoromethane in the collision-induced band of the Raman vibrational line ν1=908 cm−1. For the first time, binary isotropic intensities of the ν1-Raman band are reported in absolute units for Stokes frequency shifts up to 110 cm−1. From comparison with theoretical semiclassical computations of the dipole-multipole spectrum contributions, evaluations of the first derivatives of the successive dipole-multipole polarizability tensors are provided. These results are coherent with those obtained from corresponding depolarized intensities. Moreover, the agreement with ab initio quantum-chemistry calculations of the CF4 multipolar polarizabilities is satisfactory.