Pascale Roy

Signatures of the hydrogen bonding in the infrared bands of water.

Infrared spectroscopy measurements have been completed over a wide range of frequencies allowing to measure the evolution of both intramolecular and intermolecular vibrational modes in water as a function of temperature. Emphasis is made on the high frequency OH stretching band and the so-called connectivity band that lies in the far infrared region. The substructures of the two infrared bands are analyzed in terms of different levels of connectivity of the water molecules, along the statements of the percolation model. Both band profiles appear to be related to the different degrees of connectivity of water molecules. Comparison of the data with the predictions of the percolation model shows good agreement as for the temperature evolution of liquid water. This work provides additional support to the interpretation of water bands substructures as signatures of its very specific connectivity pattern.

POLARONIC OPTICAL ABSORPTION IN ELECTRON-DOPED AND HOLE-DOPED CUPRATES

Polaronic features similar to those previously observed in the photoinduced spectra of cuprates have been detected in the reflectivity spectra of chemically doped parent compounds of high-critical-temperature superconductors, both {ital n} type and {ital p} type. In Nd{sub 2}CuO{sub 4{minus}{ital y}} these features, whose intensities depend both on doping and temperature, include local vibrational modes in the far infrared and a broad band centered at {approximately} 1000 cm{sup {minus}1}. The latter band is produced by the overtones of two (or three) local modes and is well described in terms of a small-polaron model, with a binding energy of about 500 cm{sup {minus}1}. Most of the above infrared features are shown to survive in the metallic phase of Nd{sub 2{minus}{ital x}}Ce{sub {ital x}}CuO{sub 4{minus}{ital y}}, Bi{sub 2}Sr{sub 2}CuO{sub 6}, and YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital y}}, where they appear as extra-Drude peaks. The occurrence of polarons is attributed to local modes strongly coupled to carriers, as shown by a comparison with tunneling results. {copyright} {ital 1996 The American Physical Society.}

Evolution of a Polaron Band through the Phase Diagram ofNd2−xCexCuO4−y

The evolution with doping and temperature of the polaronic absorption in a family of high-T

Experimental and theoretical study of configuration interaction states of CO+2

_c

Stabilization of different conformers of bis(trifluoromethanesulfonyl)imide anion in ammonium-based ionic liquids at low temperatures.

superconductors is first followed here across the whole phase diagram. The polaron band softens with increasing doping, is still present in the superconducting phase, and vanishes in the overdoped metallic phase. These results point toward the existence of polaron aggregates at low temperature and may provide an experimental ground for the increasing number of theoretical descriptions of many-polaron systems.

Self-assembly of bridged silsesquioxanes: modulating structural evolution via cooperative covalent and noncovalent interactions.

Configuration interaction states of CO+2 have been observed as satellites in a high resolution photoelectron spectrum of CO2 using an angle resolved electron spectrometer and far UV synchrotron radiation in the 30–55 eV photon energy range. Ten satellites have been identified in the 22–40 eV binding energy region and classified as the result of outer and inner valence ionization processes on the basis of their asymmetry parameter ( β) values. Theoretical calculations of configuration interaction states of CO+2 using an ab‐initio SCF‐CI method show that three‐hole‐two‐particle excited configurations are necessary to explain the line positions and intensities. The calculated satellite spectrum, corrected for transition moments at 45 and 1254 eV, shows an excellent agreement with experiment and allows assignments of both outer and inner valence satellite lines, with Πg, Πu, Σ+g, and Σ+u symmetries.

Polaron imprints in the infrared spectra of Nd2CuO4−y

The infrared absorption spectra of two ionic liquids with bis(trifluoromethanesulfonyl)imide (TFSI) as an anion and ammonium with different alkyl chains as cations are reported as a function of temperature. Using the comparison with ab initio calculations of the infrared-active intramolecular vibrations, the experimental lines were ascribed to the various ions composing the ionic liquids. In the liquid state of the samples, both conformers of the TFSI ion are present. In the solid state, however, the two conformers survive in N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), while only cis-TFSI is retained in N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide (TMHA-TFSI). We suggest that the longer alkyl chains of the former compound stabilize the less stable conformer of TFSI by means of stronger interactions between anions and cations.

A new, low temperature long-pass cell for mid-infrared to terahertz spectroscopy and synchrotron radiation use

The self-assembly of a bis-urea phenylene-bridged silsesquioxane precursor during sol-gel synthesis has been investigated by in situ infrared spectroscopy, optical microscopy, and light scattering. In particular, the evolution of the system as a function of processing time was correlated with covalent interactions associated with increasing polycondensation and noncovalent interactions such as hydrogen bonding. A comprehensive mechanism based on the hydrolysis of the phenylene-bridged organosilane precursor prior to the crystallization of the corresponding bridged silsesquioxane via H-bonding and subsequent irreversible polycondensation is proposed.

Vibrational spectrum and structure of silicon trioxide SiO3: A matrix isolation infrared and density functional theory study

Abstract In addition to four Eu phonons, Nd2CuO4-y single crystals show far-infrared reflectivity peaks which depend on temperature and y. They provide evidence for the insurgence of local modes induced by doping. The so called d- or J-band at ∼ 1000 cm-1 can be partially resolved, and shown to be produced by combination bands of those local modes. These results provide direct evidence for polaron formation in this compound.

Synchrotron radiation study of vibrationally resolved partial photoionization cross sections of CO2 between 64 and 80 nm

A new cell has been designed for accurate spectroscopic measurements in the 80-400 K temperature range with variable path lengths from 3 to more than 141 m. The spectral coverage at these temperatures ranges from the visible to less than 10 cm(-1), thanks to the use of diamond windows. The design of the cryostat and vacuum setups allows vibration-free operation. The equipment provides temperature homogeneity and pressure control to better than 2% over the 100-400 K and the 0.1-1000 mbar ranges. Remote-controlled opto-mechanical systems enable in situ adjustments as well as changes of the optical path length within half an hour, in order to optimize measurement time in an open user facility. It allows then to meet the specific requirements of high resolution measurements on the Far-Infrared AILES beamline at SOLEIL as well at the LISA facility, in Créteil, in the mid-IR. This new instrument opens up the way for many experiments in the field of high-resolution gas-phase IR spectroscopy, in particular, in quantitative spectroscopy for atmospheric applications: measurements of absorption line parameters (absolute intensities, cross sections, and pressure-induced widths) using Fourier transform spectroscopy. The design and performance of the equipment are briefly presented and illustrated on spectroscopic examples.