Étude par diffusion incohérente des neutrons de la dynamique de molécules cycliques en phase liquide

A la suite de l'étude par diffusion incohérente des neutrons de la dynamique moléculaire du cyclopropane, du cyclopentène et du 1,4,7,10,13,16 hexaoxacyclooctane (18 CROWN 6) à l'état liquide, nous rappelons les principaux résultats obtenus sur les mouvements de translation et de rotation de ces molécules ainsi que sur la dynamique conformationnelle des deux dernières.Nous avons essayé de faire une analyse critique de l'apport de la diffusion incohérente des neutrons et des perspectives d'études offertes par cette technique sur les molécules qui sont le siège d'une dynamique conformationnelle rapide

Electrochemistry and confocal Raman microspectrometry

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Revisited vibrational assignments of imidazolium-based ionic liquids

Imidazolium-based ionic liquids (ILs) involving anions of variable coordinating strength have been investigated using infrared (IR) and Raman spectroscopies, density functional theory (DFT) calculations and selective deuteration of the imidazolium CH groups. Particular emphasis has been placed on the vibrational assignments of the anion and cation internal vibrations, a prerequisite before any interpretation of spectral changes due to ion-ion interactions in these unconventional liquids. The vibrations of highly symmetric and weakly coordinating anions, such as PF(6)(-), have unperturbed wavenumbers, but unexpected IR or Raman activity for some modes, showing that the anion is subjected to an anisotropic electric field. The stretching as well as the in-plane and out-of-plane bending modes of the imidazolium CH groups are anharmonic. They give broad bands that reflect a large distribution of interactions with the surrounding anions. All the bending modes are mixed with ring vibrations and the stretching modes are complicated by Fermi resonance interactions with overtones and combination of in-plane ring modes. However, the stretching vibration of the quasi-diatomic C((2))-D bond appears to be a good spectroscopic probe of the increasing cation-anion interactions when the coordinating strength of the anion increases. The broad absorption observed in the far IR with weakly coordinating anions remains practically unchanged when the acidic C((2))-H imidazolium bond is methylated and even when the imidazolium cation is substituted by tetra-alkyl ammonium or pyrrolidinium cations. It is concluded that this absorption is a general feature of any IL, coming from the relative translational and librational motions of the ions without needing to invoke C((2))-H anion hydrogen bonds

Wide-field optical coherence tomography: Imaging of biological tissues at 1220 nm

International audienceA two-dimensional optical coherence tomography technique has been developed in order to obtain multiple longitudinal slices of a biological sample directly, in a single Z-scan. The system is based on a femtosecond Cr4+:Forsterite laser and an infrared camera for wide-field imaging of the sample with a depth resolution of 9 micrometers . With this imaging apparatus, we investigated biological tissues such as human skin, human tooth and a mouse ear to observe the different constitutive tissues of the samples

Wide-field optical coherence tomography: imaging of biological tissues

We describe a two-dimensional optical coherence tomography technique with which we were able to obtain multiple longitudinal slices of a biological sample directly in a single Z scan. The system is based on a femtosecond Cr4+:forsterite laser and an infrared camera for wide-field imaging of the sample with a depth resolution of 5 µm. With this imaging apparatus we were able to investigate human skin and mouse ear samples and to observe the different constitutive tissues