Nicole Le Calvé

Spectres de vibration du trans-azoxybenzène et de quelques dérivés isotopiques

Abstract The I.R. (50–3200 cm −1 ) and Raman (100–3200 cm −1 ) spectra of the trans -azoxybenzenes C 6 H 5 NONC 6 H 5 , C 6 D 5 NONC 6 D 5 and C 6 H 5 N 15 ON 15 C 6 H 5 have been analyzed. The infrared dichroism of an oriented crystal of C 6 H 5 NONC 6 H 5 and C 6 D 5 NONC 6 D 5 has been also observed between 300 and 1600 cm −1 . An assignment of the fundamental vibrations is proposed. The electronical delocalization between the phenyl and the azoxy groups is discussed.

Vibrational study of various crystalline phases of thallium dihydrogen phosphate TlH2PO4 and its deuterated analog TlD2PO4

Abstract Vibrational spectra of thallium dihydrogen TlH 2 PO 4 and dideuterium TlD 2 PO 4 phosphates have been obtained in the 4000-10 cm −1 region as a function of temperature between 5 and 460 K. FT infrared absorption, Raman and inelastic neutron scattering spectra of polycrystalline samples are reported. Single crystals of TlH 2 PO 4 were studied by reflection in the infrared and Raman spectroscopies. The spectra reveal two structural first-order phase transitions at ≈ 357 and ≈ 230 K for TlH 2 PO 4 and ≈ 400 and ≈ 350 K for TlD 2 PO 4 . In addition there is another transition at 127 K for TlD 2 PO 4 . This latter one is an order-order type transition while the other two correspond to successive ordering of the O.H…O hydrogen bonds and to orientation of the PO 4 tetrahedra. The three hydrogen bonds and the Tl + crystalline sites appear to be more similar in TlD 2 PO 4 than in TlH 2 PO 4 . The sequences of phase transitions in both compounds are compared. TlH 2 PO 4 may become ferrielectric at low temperature. The unusual behaviour of TlH 2 PO 4 at low temperature (6 K) which exists as a highly disordered phase and gives an ordered phase at higher temperature may be related to the high deformability of the Tl + ions.

Polymorphisme Cristallin des Sept Premiers Termes de la Serie des 4,4′-Di-n-alcoxyazoxybenzenes—I—Enthalpimetrie Differentielle—Spectroscopie Raman (Modes de Reseau)

Abstract A crystalline polymorphism has been detected in the seven first members of the homologous series 4,4′-di-n-alkoxyazoxybenzenes (n = 1 to 7) by D.S.C and Raman spectroscopy. In the case of the compounds n = 1,3,4,5, the crystalline polymorphism is characterized in the high temperature phase by a statistical disorder of the azoxy group, the molecules being pseudo-centrosymmetrical. Besides, for n = 3 and 5, con-trarily to n = 1 and 4, an important increase of the molecular volume due to conformational changes appears at the transition. As for the members n = 2, 6 and 7, the crystalline systems of the two solids are practically similar.

Spectres de vibration de dérivés polyphénylés: triphénylméthanol, triphénylarsénozyde, diphénylsnlfoxyde et diphénylsélénoxyde à l'état solide entre 40 et 1600 cm−1: Complexes du triphénylméthanol avec les oxydes

Abstract Infrared and Raman spectra of triphenylmethanol, triphenylarsenoxide, diphenylsulfoxide and diphenylselenoxide have been analyzed in solid state between 40 and 1600 cm−1. An assignment of the observed frequencies is proposed. The spectra of the TPCOH(OD) complexes with bases TPASO, DPSO and DPSeO have been also recorded. The effect of the hydrogen bond is the most important on the vibrations of the OH(OD) group.

Spectres de vibration du p-azoxyanisole dans les phases solide et nématique

Abstract A new assignment of internal and external vibrations of crystalline p-azoxy-anisole is proposed. The spectral variations observed for different phases, in particular in the Raman spectra below 100 cm−1, are discussed.

Vibrational study by inelastic neutron scattering, infrared absorption and Raman scattering of potassium, rubidium and cesium dihydrogenarsenate crystals: Comparison with thallium dihydrogenarsenate

Abstract The vibrational study of polycrystalline potassium, rubidium and cesium dihydrogenarsenates, KH2AsO4 RbH2AsO4 and CsH2AsO4, has been undertaken in the 20–4000 cm−1 range. The inelastic neutron scattering spectra obtained at 20 K allow a precise assignment of the OH vibrations. The infrared absorption and Raman scattering spectra of the paraelectric and ferroelectric phases have been analyzed. The three compounds are isomorphous with KH2PO4. The results are compared to those obtained for the thallium dihydrogenarsenate TlH2AsO4. In all compounds the proton dynamics appear weakly coupled to heavy atoms motions. The order-disorder transition at Tc is associated to relational motions of anions and protons in the tetragonal potassium, rubidium and cesium dihydrogenarsenates and to collective reorientational motions of anions in monoclinic thallium derivative. The spectroscopic features show the participation of cations Kt, Rb+ and Cs+ to the dynamics of the three-dimensional lattice in both phases. In contrast, heavy-cation Tl+ motions are decoupled from the dynamics of hydrogen bond layers. No correlation between ordering of lattice and OH stretching wavenumber is observed.

Polymorphisme Cristallin des Sept Premiers Termes de la Serie des 4,4′-Di-n-alcoxyazoxybenzenes—II—Etude des Modes Internes (Spectroscopies Infrarouge et Raman)

Abstract A study of the infrared and Raman spectroscopic changes occurring in the frequency range 200–1600 cm−1 at the solid-solid or solid-liquid crystal transitions of the homologous series of 4,4′-di-n-alkoxyazoxybenzenes (n – 1 to 1) has enabled us to determine their molecular configurations in the solid phases and the liquid crystal state. In the low temperature solid phase, the alkoxy tails of the n = 2,3, 5,7 compounds have an all-trans configuration whereas those of the n = 4 and 6 compounds show g± or g± tg± defects. Some kind of configurational change appears at the crystal polymorphic transition for n = 3, 4, 5 and at the mesomorphic transition for n = 6 and 7 according to the relative importance of the enthalpic and entropic variations of the crystal-crystal or crystal-liquid crystal transition. As to the n = 1 and 2 compounds, it seems that the perturbations observed are related to a statistical disorder of the azoxy group rather than the two possible orientations of the methoxy or ethoxy gro...

Caractérisation Spectroscopique d'une Phase Haute Temperature du Parachlorophénol

Abstract A high temperature phase of parachlorophenol (phase γ) has been investigated by infrared and Raman spectroscopy. It can be shown that the molecules are linked in infinite chains by hydrogen bonds and that there are eight equivalent molecules in the unit cell. Une phase haute temperature (phase γ) du parachlorophenol est etudiee par spectrometrie infrarouge et Raman. II est montre que les molecules sont liees par liaison hydrogene en chaines infinies et que la maille primitive contient huit molecules equivalentes.