Isotropic and anisotropic collision-induced Raman scattering by monoatomic gas mixtures: Ne-Ar

We report the long-overdue collision-induced Raman scattering spectrum by a pair of unlike rare gas atoms. Absolute-unit scattering intensities, both isotropic and anisotropic, are given for Ne-Ar, along with the depolarization ratio for this system, recorded by a gaseous room-temperature mixture over a wide range of frequency shift. We make a critical comparison with spectra computed quantum-mechanically on the basis of modern pair-polarizability representations for Ne-Ar, of either ab initio or density functional theory methods. We report a value for the Kerr second virial coefficient, deduced from our measurements. Our data are especially intended to add to the vital yet hitherto incomplete knowledge of the role of collision-induced processes in atmospheric environments

Collision-induced Raman scattering by rare-gas atoms: The isotropic spectrum of Ne–Ne and its mean polarizability

We report the room-temperature isotropic collision-induced light scattering spectrum of Ne–Ne over a wide interval of Raman shifts, and we compare it with the only available experimentalspectrum for that system as well as with spectra calculated quantum-mechanically with the employ of advanced ab initio -computed data for the incremental mean polarizability. Thespectral range previously limited to 170 cm−1 is now extended to 485 cm−1 allowing us to successfully solve the inverse-scattering problem toward an analytic model for the meanpolarizability that perfectly matches our measurements. We also report the depolarization ratio of the scattering process, lingering over the usefulness of this property for more stringent checks between the various polarizability models

Anisotropic collision-induced Raman scattering by Ne-Ne: Evidence for a nonsmooth spectral wing

We report the anisotropic collision-induced scattering (CIS) spectrum of two neon atoms at room temperature. The covered spectral range hitherto restricted to 170 cm−1 is here tripled. Both our measurements and quantum-mechanical calculations obtained on the basis of large-scale ab initio anisotropy representations reveal a well-defined saddle-shaped wing. This peculiar structure is experimental evidence of a binary CIS line shape with an aspect other than a smooth wing in a logarithmic plot. Equally interesting is the fact that this feature has been predicted (though only qualitatively) by the simple semiempirical model long ago reported by Meinander, Tabisz and Zoppi J. Chem. Phys. 84 3005 (1986), but no emphasis had at that time been placed on the aspect of the wing of the model spectrum probably due to the lack of high-frequency experimental data

Collision-induced Raman scattering and the peculiar case of neon: Anisotropic spectrum, anisotropy, and the inverse scattering problem

Owing in part to the p orbitals of its filled L shell, neon has repeatedly come on stage for its peculiar properties. In the context of collision-induced Raman spectroscopy, in particular, we have shown, in a brief report published a few years ago [M. Chrysos et al., Phys. Rev. A 80, 054701 (2009)], that the room-temperature anisotropic Raman lineshape of Ne–Ne exhibits, in the far wing of the spectrum, a peculiar structure with an aspect other than a smooth wing (on a logarithmic plot) which contrasts with any of the existing studies, and whose explanation lies in the distinct way in which overlap and exchange interactions interfere with the classical electrostatic ones in making the polarizability anisotropy, α ∥ − α ⊥. Here, we delve deeper into that study by reporting data for that spectrum up to 450 cm−1 and for even- and odd-order spectral moments up to M 6, as well as quantum lineshapes, generated from SCF, CCSD, and CCSD(T) models for α ∥ − α ⊥, which are critically compared with the experiment. On account of the knowledge of the spectrum over the augmented frequency domain, we show how the inverse scattering problem can be tackled both effectively and economically, and we report an analytic function for the anisotropy whose quantum lineshape faithfully reproduces our observations

Anisotropic collision-induced Raman scattering by the Kr:Xe gas mixture

We report anisotropic collision-induced Raman scattering intensities by the Kr–Xe atomic pair recorded in a gas mixture of Kr and Xe at room temperature. We compare them to quantum-mechanical calculations on the basis of modern incremental polarizability models of either ab initio post-Hartree–Fock or density functional theory methods

The isotropic remnant of the CO2 near-fully depolarized Raman 2v3 overtone

In a recent paper [M. Chrysos, I. A. Verzhbitskiy, F. Rachet, and A. P. Kouzov, J. Chem. Phys. 134, 044318 (2011)], we showed that, in CO2, the 2 nu(3) transition generates a Raman line spectrum that is 98% depolarized, a property in agreement with general symmetry rules. Here, we present an extensive analysis, experimental and theoretical, of the isotropic remnant of this overtone. The isotropic spectrum turned out to be 45 times less intense than its anisotropic counterpart and to have a moment that is 350 times smaller than the moment of the anisotropic spectrum, in excellent agreement with theoretical predictions. Once the measured intensity (along with other data exclusively experimental) was fed back into the formula of the moment, a value for the CO2 mean-polarizability asymmetric stretch derivative partial derivative(2)(alpha) over bar/partial derivative q(3)(2) was returned that matches the best ab initio prediction to better than 4%. Agreement, in order of magnitude, was found between the intensity reported herein and that reported in the sole prior study of this overtone [G. Tejeda, B. Mate, and S. Montero, J. Chem. Phys. 103, 568 (1995)]. (C) 2011 American Institute of Physics. [doi:10.1063/1.3557820

Heavy rare-gas atomic pairs and the “double penalty” issue: Isotropic Raman lineshapes by Kr2, Xe2, and KrXe at room temperature

We report absolutely calibrated isotropic Raman lineshapes for Kr2 and Xe2 and for KrXe at 294.5 K and compare them to quantum-mechanically generated lineshapes by using state-of-the-art second-order Møller-Plesset and DFT/B3LYP data sets for the induced mean dipole polarizability ᾱ  . A very good agreement between the numerical and the experimental data was observed but the large uncertainty margins and the short Raman frequency interval probed in our experiment prevented us from rating on a more refined scale the performance of the tested ᾱ  models. These drawbacks are inherent in isotropic Raman spectrum measurements and amplified for dissimilar pairs because, for such systems and spectra, the unreliable operation of subtracting optical signals of comparable magnitude occurs twice per Raman frequency shift value, thus penalizing twice the quality of the measured data. In light of our findings and of previously reported evidence about related electric properties in Kr2 and Xe2 and in KrXe, we are left with no doubt as to the consistency of the induced-polarizability and interatomic-potential data used for these three systems at the reported level of accuracy