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Vibron and roton bands in the first overtone of solid and liquid parahydrogen
No full textThe infrared spectrum of the rotovibrational band v=0→2 of parahydrogen has been observed in the condensed phases down to T=2 K. In the solid, phonon and roton sidebands exhibit peaks corresponding to those observed in the fundamental. Contributions arising from the reorientation of ortho-H2 impurities have been detected. The Q1(0)+S1(0) band has been resolved into an asymmetric doublet, and the origin of this latter is discussed. In the liquid phase the observed line shapes include strong translational contributions, and are accounted for by assuming that at short times the excited molecule is encapsulated in the cage of nearest neighbors. © 1994 The American Physical Society
Routes to gelation in a clay suspension
No full textThe gelation of water suspension of a synthetic clay (Laponite) has been studied by dynamic light scattering in a wide range of clay weight concentration (C-w=0.003-0.031). At variance with previous determination, indicating a stable liquid phase for C-w<C(w)(*)approximate to0.015-0.018, we find that gelation actually takes place in the whole examined C-w range. We find also that C-w(*) marks the transition between two different routes to gelation. We hypothesize that at low concentration Laponite suspension behaves as an attractive colloid and that the slowing down of the dynamics is attained by the formation of larger and larger clusters while at high concentration the basic units of the arrested phase could be the Debye Huckel spheres associated with single Laponite plates
About the formation of C60 fine particles with reprecipitation method in ethanol/carbon disulfide mixture.
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TRANSLATIONAL AND ROTATIONAL SPECTRA IN THE FUNDAMENTAL INFRARED BAND OF LIQUID AND SOLID PARAHYDROGEN
No full textThe Q1(0) and Q1(0)+S0(0) infrared bands have been studied in liquid and solid para-H-2 with particular regard to their translational sidebands. In the liquid, their line shapes are well fitted by a model in which the excited particle is encapsulated. In the solid, the phonon sidebands reproduce the main features of the density of states (DOS), as extracted from neutron scattering. The S1(0)+S0(0) band shows a pure rotonic line shape which is well described by recent DOS calculations
Polaronic optical absorption in semiconducting and superconducting oxides
No full textThe infrared and Raman spectra of High-Tc superconductors (HCTS) in the normal phase exhibit vibrational modes (IRAV) which are superimposed to a Drude background from high-mobility carriers. In the far infrared the IRAV appear as well-resolved peaks, shifted in energy with respect to the normal modes of the lattice. In the midinfrared they are grouped into a broad polaron band peaked at about 0.1 eV. At corresponding energies, in the semiconducting phase one observes bands that are unambiguously identified as polaronic. Moreover, the IRAV show remarkable correspondences with the peaks in the Eliashberg function as determined in the same systems by tunneling measurements. These results point towards the existence of two types of carriers in HCTS, one at least being polaronic in nature
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