Greenhouse effects and the collision induced bands by the autoperturbed carbon dioxide

Date du colloque&nbsp;: 07/2008</p

Collision-induced Raman scattering from a pair of dissimilar particles: An intriguing mathematical model predicting the suppression of the odd-numbered partial waves

Relying on a simple analytic two-atom model in which the anisotropy of the interaction dipole polarizability obeys an inverse power law as a function of separation, we offer mathematical and numerical evidence that, in a monoatomic gas, the free-free Raman spectrum for a collisional pair of two different isotopes,a–a′, may vastly differ from that for a–a. This result is obtained even if a and a′ are assumed to have the same mass and zero nuclear spin and even if a–a and a–a′ are subject to the same interaction polarizability and potential. The mechanism responsible for this effect is inherent in the parity of the partial-wave rotational quantum number J: given that the contribution of each partial wave to the Raman cross section is controlled by a polarizability-transition matrix-element and that each of those matrix-elements has a radial component with a magnitude slightly smaller than that of the preceding partial wave, a deficit which disfavors the odd-numbered waves is accumulated upon summing over J. In the far high-frequency wing, this deficit tends to generate spectral intensities for a–a′ about half as great as the a–a ones, a tendency which becomes all the more effective as temperature is decreased. We show for instance that, for the spectral branch ΔJ = 2, the fractional difference between the free-free differential cross sections for a–a and a–a′ is 12(1−x2)31+3x412(1−x2)31+3x4, with x=E/E′−−−−−√x=E/E′ (E (E′) being the initial (final) state energy of the pair and E′ − E = hcν (ν &gt; 0)). Remarkably, this quantity is zero at ν ≈ 0 but goes to 1212 for ν ≫ 0. For ΔJ = 0, analogous conclusions may be drawn from the expression (1+ln(1+x1−x)2arctanx)−1(1+ln(1+x1−x)2arctanx)−1

An organisational design approach of business environments: the case of Barcamps milieu in Paris

International audienceShifting business environment is often described as a decisive factor for organisational transformations. Various levels of organisation are proposed by the literature in order for an enterprise to be able to handle factors that outreach their boundaries. In this paper, we examine the case of Barcamps, a novel organisational pattern addressing issues beyond productivity and efficiency. We propose an analysis of its design parameters and functional requirements, contributing to the research and practice of organisational design beyond the boundaries of a specific organisation

Comment on “CCSD study of anharmonic Raman cross sections of fundamental, overtone, and combination transitions”

Equations (36) and (37) in L. N. Vidal, P. A. M. Vazquez, Int. J. Quantum Chem. 2012, 112, 3205 are wrong. The agreement between theoretical and experimental Raman cross sections is greatly improved with use of the corrected expressions

Exploring the sources of innovation: the case of Hackathon

This paper advances the exploration of the sources of innovation through the characteristics of the objects produced. To achieve a greater openness to the un- known of innovation processes, we choose not to examine final products. While, as put by von Hippel, final products embed in their functions a value (of use or of exchange), they hide the non-deterministic nature of the process, implying that the goal was known from the beginning. Instead, we will examine poten- tial products, that means projects that have not yet concluded to the market, neither have they been used. Investigating the contributions at a Hackathon hosted by Google, we induce three categories of innovative attitude: collective intimacy, entrepreneurial thinking and technological avant-garde

Dirac bubble potential for He–He and inadequacies in the continuum: Comparing an analytic model with elastic collision experiments

We focus on the long-pending issue of the inadequacy of the Dirac bubble potential model in the description of He–He interactions in the continuum [L. L. Lohr and S. M. Blinder, Int. J. Quantum Chem. 53, 413 (1995)]. We attribute this failure to the lack of a potential wall to mimic the onset of the repulsive interaction at close range separations. This observation offers the explanation to why this excessively simple model proves incapable of quantitatively reproducing previous experimental findings of glory scattering in He–He, although being notorious for its capability of reproducing several distinctive features of the atomic and isotopic helium dimers and trimers [L. L. Lohr and S. M. Blinder, Int. J. Quantum Chem. 90, 419 (2002)]. Here, we show that an infinitely high, energy-dependent potential wall of properly calculated thickness rc(E) taken as a supplement to the Dirac bubble potential suffices for agreement with variable-energy elastic collision cross section experiments for 4He–4He, 3He–4He, and 3He–3He [R. Feltgen et al., J. Chem. Phys. 76, 2360 (1982)]. In the very low energy regime, consistency is found between the Dirac bubble potential (to which our extended model is shown to reduce) and cold collision experiments [J. C. Mester et al., Phys. Rev. Lett. 71, 1343 (1993)]; this consistency, which in this regime lends credence to the Dirac bubble potential, was never noticed by its authors. The revised model being still analytic is of high didactical value while expected to increase in predictive power relative to other appraisals

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

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

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

Isomerization of azobenzene and the enhancement of dynamic heterogeneities in molecular glass formers

Prompted by recent findings [Teboul, Saiddine, and Nunzi, Phys. Rev. Lett. 103, 265701 (2009); Orsi et al., Phys. Rev. E 82, 031804 (2010)] that the isomerization of few azobenzene molecules dispersed in a glass former greatly enhances the dynamic heterogeneity (DH) of the medium, we raise the issue as to whether the isomerization process gives rise to additional DHs or whether instead it stimulates the mechanisms at the origin of the thermal DHs, accelerating them in time. To this end, molecular dynamics simulations are made to study the much insightful four-point susceptibility, dynamic facilitation, and Van Hove correlation functions both when the isomerization is activated and when it is artificially switched off. Our results do not rule out any of the two scenarios as a possible cause for the enhancement of DHs upon switching on the isomerization process, but clearly show that the second one is by far the dominant mechanism in the dynamics of the supercooled liquid