T. Bancewicz

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.

The hyper-Rayleigh light scattering spectrum of gaseous Ne–Ar mixture

Hyper-Rayleigh binary collisional spectra for a Ne–Ar gaseous system are computed within the frequency range up to 500 cm−1 with four new ab initio hyperpolarizability models used. The properties of the profiles as well as the depolarization ratio frequency dependence are discussed. The contributions to the spectra given by the dipolar b1(r) and the octopolar b3(r) components of the hyperpolarizability tensor and the multipolar model HR spectrum are compared.

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.

High-frequency interaction-induced rototranslational wings of isotropic nitrogen spectra

The isotropic rototranslational scattering of nitrogen gas is studied in the frequency range 300–600 cm-1, both theoretically and experimentally, at a density of 41 and 169 amagat. The isotropic double differential cross-section for scattered light is calculated theoretically considering first- and second-order dipole-induced dipole, first-order dipole-dipole-quadrupole, and dipole-induced octopole light scattering mechanisms as well as their cross contributions. The irreducible spherical form for the induced operator of these light scattering mechanisms was determined. Good comparison is found in the frequency range 300–450 cm-1 between the theoretical and experimental double differential cross-sections. When an exponential contribution [exp(-ν/ν0)] with ν0 = 118 cm-1 is considered to model very short-range light scattering mechanisms good comparison is found over the whole frequency range.

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.

Interaction-induced pair hyperpolarizabilities by spherical irreducible tensors

Starting from the electrostatic part of the intermolecular multipole interaction energy we derived irreducible spherical tensor formulas for the first-order long-range, interaction-induced first and second pair hyperpolarizabilities ΔβLM and ΔγLM for arbitrary shape monomers. For atoms a general relation is obtained for the dipolei–2k-pole hyperpolarizability tensor Z(i+k) of arbitrary order, between its irreducible spherical components Z00[((((11)a11)a2…)ai−21)kk] and the Cartesian counterpart Zzz…z(i+k). For isotropic systems the expressions for Δβzzz and Δγzzzz are in full agreement with the Cartesian tensor results of Buckingham, Concannon and Hands [J. Phys. Chem. 98, 10455 (1994)] and Li et al. [J. Chem. Phys. 105, 10954 (1996)]. Our irreducible spherical tensor results for ΔβLM and ΔγLM are very desirable when dealing with molecular rotations, e.g., in spectral line shape calculations of interaction-induced hyper-Rayleigh and/or hyper-Raman light scattering. Finally we show how our spherical tensor...

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.

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.