Structural and Vibrational Properties of Diglyme and Longer Glymes

The conformational states of diglyme in both the solid and liquid states have been determined by an integrated use of both IR and Raman spectroscopy together with ab initio/density functional theory (DFT) calculations. Using knowledge from diglyme also made possible the study of the conformational state of longer glymes, including a quantitative study of the D-LAM mode. We hereby unambiguously can assign the (tgt)(n) conformational state to all glymes and PEO in the solid state

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

Neutron and Raman scattering studies of the methyl dynamics in solid toluene and nitromethane

Solid toluene has been studied in its α phase at 5 K by high resolution Inelastic Neutron Scattering (I.N.S.). The tunnel splitting of the methyl torsion group state has been found to be 0.196 cm-1 (24.3 μeV) for C6D5CH3 and 0.0088 cm-1 (1.1 μeV) for C6D5CD3. Simple cosine (V3 , V6) or square well potentials are able to reproduce this splitting but the calculated first torsional transitions (∼ 56 cm -1) are then slightly higher than the value of 46.8 cm-1 deduced from the analysis of the Raman and I.N.S. spectra obtained for several isotopic derivatives in a large temperature range. The possibility of coupling of the first torsional excited states with some phonons is invoked to explain these observations. A similar Raman and I.N.S. study of solid nitromethane allows the —CH3 torsion to be situated at about 53 cm-1 and leads to similar conclusions.Le toluène solide a été étudié dans sa phase α à 5 K par diffusion inélastique des neutrons à haute résolution. L'éclatement de l'état fondamental de torsion du méthyle a été trouvé de 0,196 cm-1 (24,3 μeV) pour C6D5CH3 et 0,0088 cm-1 (1,1 μeV) pour C6D5CD3. On peut rendre compte de cet eclatement par de simples potentiels cosinusoïdaux (V3, V 6) ou carrés, mais les valeurs calculées des premières transitions de torsion (∼ 56 cm-1) sont alors légèrement plus élevées que celles déduites de l'analyse des spectres Raman et neutroniques de plusieurs dérivés isotopiques étudiés dans une large gamme de température. Pour expliquer ces observations, on peut supposer que les premiers niveaux excités de torsion se couplent avec des phonons. Une étude similaire du nitrométhane solide permet de situer la torsion du groupe CH3 à environ 53 cm-1 et conduit à des conclusions analogues

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