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

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 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 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 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

Palladium-acetate catalyst for regioselective direct arylation at C2 of 3-furanyl or 3-thiophenyl acrylates with inhibition of Heck type reaction

International audiencePd(OAc)2/KOAc was found to be an efficient catalytic system for the direct arylation of thiophene and furan derivatives bearing an acrylate at C3. The selectivity of the reaction strongly depends on the nature of the coordinating base. Na2CO3 and Li2CO3 favours the Heck type reaction; whereas the use of KOAc or CsOAc promotes regioselective arylation at C2 of the heteroarene and inhibits the Heck type reaction. The direct arylation products were obtained in moderate to good yields using only 0.1 mol % of catalyst. Electron-withdrawing substituent on aryl bromide, such as acetyl, formyl, ester, nitrile or nitro, favours the reaction; whereas electron-donating ones are unfavourable

Broadband cavity-enhanced absorption spectroscopy with incoherent light

Although broadband incoherent light does not efficiently couple into a high-finesse optical cavity, its transmission is readily detectable and enables applications in cavity-enhanced absorption spectroscopy in the gas phase, liquid phase and on surfaces. This chapter gives an overview of measurement principles and experimental approaches implementing incoherent light sources in cavity-enhanced spectroscopic applications. The general principles of broadband CEAS are outlined and general “pros and cons” discussed, detailing aspects like cavity mirror reflectivity calibration or the establishment of detection limits. Different approaches concerning light sources, cavity design and detection schemes are discussed and a comprehensive overview of the current literature based on a methodological classification scheme is also presented

One pot Pd(OAc)2-catalysed 2,5-diarylation of imidazoles derivatives

International audienceThe regioselective 2- or 5-arylation of imidazole derivatives with aryl halides using palladium catalysts has been described in recent years; whereas the arylation at both C2 and C5 carbons of imidazoles in high yields has not been performed. We found conditions allowing the access to these 2,5-diarylimidazoles via a one pot reaction. The choice of the base was found to be crucial to obtain these products in high yields. Using CsOAc as the base, DMA as the solvent and only 2 mol % of the phosphine-free Pd(OAc)2 the catalyst, the target 2,5-diarylated imidazoles were obtained in moderate to good yields with a wide variety of aryl bromides. Substituents such as fluoro, trifluoromethyl, formyl, acetyl, propionyl, ester, nitro or nitrile on the aryl bromide were tolerated. Sterically congested aryl bromides or heteroaryl bromides can also be employed. Surprisingly the nature of the substituent at position 1 on the imidazole derivative exhibits a huge influence on the reaction

The near infrared cavity-enhanced absorption spectrum of methyl cyanide

The absorption spectrum of methyl cyanide (CH3CN) has been measured in the near IR between 6000 and 8000 cm(-1) with a resolution of 0.12 cm(-1) using Fourier transform incoherent broadband cavity-enhanced absorption spectroscopy. The spectrum contains several weakly perturbed spectral regions: potential vibrational combination bands contributing to the spectrum are outlined. Line positions and cross-sections of CH3CN between 6814 and 7067 cm(-1) have been measured at high-resolution of 0.001 cm(-1) using diode laser based off-axis cavity-enhanced absorption spectroscopy. A total of 4630 new absorption lines of CH3CN are identified in this region. A value for the self-broadening coefficient has determined to be (3.3 +/- 0.2) X 10(-3) cm(-1) mbar(-1) for one isolated line at 7034.171 cm(-1). Several line series have been identified in these regions and an autocorrelation analysis performed with a view to aiding future assignments of the rotational-vibrational transitions

Long optical cavities for open-path monitoring of atmospheric trace gases and aerosol extinction

An incoherent broadband cavity-enhanced absorption spectroscopy setup employing a 20 m long optical cavity is described for sensitive in situ measurements of light extinction between 630 and 690 nm. The setup was installed at the SAPHIR atmospheric simulation chamber during an intercomparison of instruments for nitrate (NO3) radical detection. The long cavity was stable for the entire duration of the two week campaign. A detection limit of similar to 2 pptv for NO3 in an acquisition time of 5 s was established during that time. In addition to monitoring NO3, nitrogen dioxide (NO2) concentrations were simultaneously retrieved and compared against concurrent measurements by a chemiluminescence detector. Some results from the campaign are presented to demonstrate the performance of the instrument in an atmosphere containing water vapor and inorganic aerosol. The spectral analysis of NO3 and NO2, the concentration dependence of the water absorption cross sections, and the retrieval of aerosol extinction are discussed. The first deployment of the setup in the field is also briefly described