Double vibrational collision-induced Raman scattering by SF6–N2: Beyond the point-polarizable molecule model

International audienceCollision-induced Raman bandshapes and zeroth-order spectral moments are calculated both for the depolarized spectrum and for the extremely weak isotropic spectrum of the SF6(ν1) +N2(ν1) double-Raman-scattering band. A critical comparison is made with experiments conducted recently by the authors [ Phys. Rev. A 81 012702 (2010) 81 042705 (2010)]. The study of this transition, hitherto restricted to the model framework of two point-polarizable molecules, is now completed to incorporate effects beyond the point-molecule approximation. Whereas the extended model offers a few percent improvement in the depolarized spectrum, it reveals a huge 80% increase in the isotropic spectrum and its moment, owing essentially to the polarizability anisotropy of N2. For both spectra, agreement between quantum-mechanical calculations and our experiments is found, provided that the best ab initio data for the (hyper)polarizability parameters are used. This refined study shows clearly the need to include all mechanisms and data to a high level of accuracy and allows one to decide between alternatives about difficult and controversial issues such as the intermolecular potential or the sensitive Hamaker force constants.</p

Evidence for double incoherent Raman scattering in binary gas mixtures: SF6-N2

International audienceWe report a collision-induced Raman band by room temperature gas mixtures of sulfur hexafluoride and nitrogen. The band is centered at the sum of the frequencies of the symmetric-stretching ν1 transition of SF6 and the fundamental transition of N2, and its intensity scales as the product of the partial densities of the gases. The observed process is evidence of double incoherent Raman scattering (DRS) by SF6-N2, in which both molecules simultaneously undergo two Raman-allowed transitions. The band was found to be almost fully depolarized, in agreement with previous observations in other systems and with theoretical predictions. Its integrated intensity is about one-third higher than the total area predicted by the leading-order dipole-induced dipole model. This discrepancy suggests that DRS is a practical means of assessing the quality of intermolecular potential models, which, in the case of SF6-N2, is still believed to be not good enough. Our work is expected to open the door to a multitude of studies involving complicated processes encountered in nonpolar gases and their mixtures, which are of direct relevance to atmospheric research.</p

Spin dynamics study in layered van der Waals single-crystal Cr2Ge2Te6

We study the magnetization dynamics of a bulk single crystal Cr2Ge2Te6 (CGT), by means of broadband ferromagnetic resonance (FMR), for temperatures from 60 K down to 2 K. We determine the Kittel relations of the fundamental FMR mode as a function of frequency and static magnetic field for the magnetocrystalline easy—and hard—axis. The uniaxial magnetocrystalline anisotropy constant is extracted and compared with the saturation magnetization, when normalized with their low temperature values. The ratios show a clear temperature dependence when plotted in the logarithmic scale, which departs from the predicted Callen-Callen power law fit of a straight line, where the scaling exponent n, Ku (T ) ∝ [Ms (T )/Ms(2 K)]n, contradicts the expected value of 3 for uniaxial anisotropy. Additionally, the spectroscopic g factor for both the magnetic easy—and hard—axis exhibits a temperature dependence, with an inversion between 20 K and 30 K, suggesting an influence by orbital angular momentum. Finally, we qualitatively discuss the observation of multidomain resonance phenomena in the FMR spectras, at magnetic fields below the saturation magnetization