High-pressure Raman and infrared spectroscopy of polyacetylene (original) (raw)

Raman spectroscopic study of the high-pressure phase of polyethylene

Macromolecules, 1981

  1. Cotton, J. P.; Farnoux, B.; Jannink, G.; Strazielle, C. J. Polym. Sci., Polym. Symp. 1973, No. 42, 981. (5) Cotton, J. P.; Farnoux, B.; Jannink, G. J. Chem. Phys. 1972, 57, 290. Daoud, M.; Cotton, J. P.; Farnoux, B.; Jannink, G.; Sarma, G.; Benoit, H.; Duplessix, R.; Picot, C.; de Gennes, P. G. Macromolecules 1975, 8, 804. (6) Berrv. G. C.: Nakavasu. H.: Fox. T. G. J. Polvm. Sci.. Polvm. . , , , I " Phyi.'Ed. 1979,l f, 1825. (7) Nvstrom, B.; Porsch, B.; Sundelof, L.-0. Eur. Polym. J. 1977, 13, 683. 'Nystrom, B.; Roots, J.; Bergman, R. Po-lymer 1979, 20, 157. Roots, J.; Nystrom, B.; Sundelof, L.-0.; Porsch, B. ABSTRACT: The Raman spectra of polyethylene at 5.1 kbar were obtained as a function of increasing temperature in the orthorhombic, intermediate, and melt phases. It was found that a plot of r = Z(1130)/Z(1090), an order parameter related to the relative concentration of trans bonds, vs. temperature, T, was sigmoidal. The steepest change of r with T occurred in the intermediate phase. Comparison of r values in the intermediate phase with an approximate calibration curve and with values obtained from lipid membrane phase transition data indicates that the intermediate phase has significant but variable trans bond population, ranging from 6 2 to 68%. Analysis of the high-frequency C-H stretching region, which is indicative of changes in lateral

High-pressure Raman studies of ultra-high-molecular-weight polyethylene

Polymer, 1990

This paper reports the Raman spectra of ultra-high-molecular-weight polyethylene (UHMWPE) at room temperature and under high pressure employing a Mao-Bell type of miniature diamond-sapphire anvil cell. Davydov splitting near 1065 cm-1 and resonance interactions in the bending (1440-1470cm-1) and C-H stretching (2840-2950cm -1) regions of the Raman spectra of UHMWPE at high pressure are described. The dependences of mode GriJneisen parameters (ri) on vibrational frequency (vi) were determined at several pressures from the Raman spectra and compression experiments of UHMWPE. (

Raman and infrared spectroscopy of pyridine under high pressure

Physical Review B, 2010

We report the structural transitions of pyridine as a function of pressure up to 26 GPa using in situ Raman spectroscopy and infrared absorption spectroscopy. By monitoring changes in the Raman shifts in the lattice region as well as the band profiles in both Raman and IR spectra, a liquid-to-solid transition at 1 GPa followed by solid-to-solid transitions at 2, 8, 11, and 16 GPa were observed upon compression. These transitions were found to be reversible upon decompression from 22 GPa. A further chemical transformation was observed when compressed beyond 22 GPa as evidenced by the substantial and irreversible changes in the Raman and infrared spectra, which could be attributed to the destruction of the ring structure. The observed transformations in pyridine were also compared to those for benzene. The similar transition sequence with well-aligned transition pressures suggests that these isoelectronic aromatics may have similar structures and stabilities under high pressure.

High-pressure vibrational properties of polyethylene

The Journal of Chemical Physics, 2010

The pressure evolution of the vibrational spectrum of polyethylene was investigated up to 50 GPa along different isotherms by Fourier-transform infrared and Raman spectroscopy and at 0 K by density-functional theory calculations. The infrared data allow for the detection of the orthorhombic Pnam to monoclinic P2 1 /m phase transition which is characterized by a strong hysteresis both on compression and decompression experiments. However, an upper and lower boundary for the transition pressure are identified. An even more pronounced hysteresis is observed for the higherpressure transition to the monoclinic A2/m phase. The hysteresis does not allow in this case the determination of a well defined P-T transition line. The ambient structural properties of polyethylene are fully recovered after compression /decompression cycles indicating that the polymer is structurally and chemically stable up to 50 GPa. A phase diagram of polyethylene up to 50 GPa and 650 K is proposed. Analysis of the pressure evolution of the Davydov splittings and of the anomalous intensification with pressure of the IR active wagging mode provides insight about the nature of the intermolecular interactions in crystalline polyethylene.

Pressure-Induced Structural Transition in n-Pentane: A Raman Study

The Journal of Physical Chemistry B, 2007

Pressure-induced Raman spectroscopy studies on n-pentane have been carried out up to 17 GPa at ambient temperature. n-Pentane undergoes a liquid-solid transition around 3.0 GPa and a solid-solid transition around 12.3 GPa. The intensity ratio of the Raman modes related to all-trans conformation (1130 cm-1 and 2850 cm-1) to that of gauche conformation (1090 cm-1 and 2922 cm-1) suggests an increase in the gauche population conformers above 12.3 GPa. This is accompanied with broadening of Raman modes above 12.3 GPa. The high-pressure phase of n-pentane above 12.3 GPa is a disordered phase where the carbon chains are kinked. The pressure-induced order-disorder phase transition is different from the behavior of higher hydrocarbon like n-heptane.

High-pressure study of isoviolanthrone by Raman spectroscopy

The Journal of chemical physics, 2014

Vibrational properties of isoviolanthrone are investigated by Raman scattering at pressures up to 30.5 GPa and room temperature. A complete characterization of phonon spectra under pressure is given for this material. The onset of a phase transition at 11.0 GPa and the formation of a new phase above 13.8 GPa are identified from both the frequency shifts and the changes in the full width half maxima of the intra- and internal modes. The transition is proposed to result from the changes of intra- and intermolecular bonding. The tendencies of the intensity ratios with pressure are in good agreement with the pressure dependence of the resistance at room temperature, indicating that the phase transition may be an electronic origin. The absence of the changes in the lattice modes indicates that the observed phase transition is probably a result of the structural distortions or reorganizations. The reversible character of the transition upon compression and decompression is determined in t...

Raman spectroscopic study of cyclopentane at high pressure

The Journal of Chemical Physics, 2009

The behavior of cyclopentane with pressure has been investigated to 21.5 GPa using Raman spectroscopy. Various phases were observed with pressure which included liquid, two plastic, and one true crystalline phases of cyclopentane during compression and decompression sequences. Optimized molecular structure and Raman and IR vibrational spectra of the most stable puckered-ring conformation of the cyclopentane molecule were also computed using density functional theory methods. The theoretically calculated values as well as the experimentally determined pressure dependencies of spectral bands are in very good agreement with the low temperature measurements and previous mode assignments. The phase diagram of cyclopentane was analyzed with respect to pressure-induced alterations in Raman spectra across the phase boundaries. The various forms of "frozen-in" conformations in phase III are suggested to explain previous results related to existence of a "new" phase between plastic crystalline phase II and monoclinic phase III in solid cyclopentane.

High pressure Raman studies on the structural conformation of oligophenyls

Synthetic Metals, 2001

The goal of this combined experimental and computational study is to investigate the structural conformation of oligo(para-phenylenes) in the crystalline phase, in particular the planarity of this type of molecules. To this end we have performed Raman experiments on paraterphenyl and para-quaterphenyl in a pressure range from 0 to 70 kbar and at temperatures from 10 to 300 K. The positions and the relative intensities of the C±C interring stretch mode at 1280 cm À1 and the C±H in-plane bend mode at 1220 cm À1 have been tracked. We ®nd that upon increasing temperature at ambient pressure the intensity ratio I 1280 /I 1220 drops rapidly at temperatures that coincide with the crystallographic phase transition for the investigated materials. At ambient temperature also, this intensity ratio drops rapidly upon increasing pressure up to about 15 kbar. In the computational part, the Raman frequencies and activities of isolated 3P and 4P molecules were calculated within restricted Hartree±Fock formalism with the interring tilt angles varying from 0 to 908. These calculations con®rm that the I 1280 /I 1220 intensity ratio can be related to the planarity of the molecules. Three-dimensional bandstructure calculations within density functional theory were applied to determine phonon frequencies and estimate Raman activities for the polymer poly(paraphenylene). These simulations show that the same conclusions hold for crystalline environment. # 2001 Published by Elsevier Science B.V.

X-ray Raman Spectroscopic Study of Benzene at High Pressure

The Journal of Physical Chemistry B

We have used X-ray Raman spectroscopy (XRS) to study benzene up to ∼20 GPa in a diamond anvil cell at ambient temperature. The experiments were performed at the High-Pressure Collaborative Access Team's 16 ID-D undulator beamline at the Advanced Photon Source. Scanned monochromatic X-rays near 10 keV were used to probe the carbon X-ray edge near 284 eV via inelastic scattering. The diamond cell axis was oriented perpendicular to the X-ray beam axis to prevent carbon signal contamination from the diamonds. Beryllium gaskets confined the sample because of their high transmission throughput in this geometry. Spectral alterations with pressure indicate bonding changes that occur with pressure because of phase changes (liquid: phase I, II, III, and III′) and possibly due to changes in the hybridization of the bonds. Changes in the XRS spectra were especially evident in the data taken when the sample was in phase III′, which may be related to a rate process observed in earlier shock wave studies.

Infrared Absorption Studies of n-Heptane under High Pressure

The Journal of Physical Chemistry B, 2003

Mid-infrared spectra of neat n-heptane at room temperature are presented over a pressure range from ambient to 70 kbar. The application of hydrostatic pressure induces frequency shifts, band splittings, and significant changes in the line shapes of internal vibrational modes both in liquid and in solid phases. The results are discussed in terms of the liquid-solid phase transition and changes of the population of molecular conformers. Evidence for a solid-solid phase transition near 30 kbar is also presented.