Spectroscopic studies of molecular interaction at the liquid–liquid interface (original) (raw)
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Chemical Physics, 2000
Raman spectra of the stretching mode m S (CBC) (A g) at 2224 cm À1 , the C±Ph bending in plane mode (B 3g) at 535 cm À1 , the low frequency Raman region from 15±200 cm À1 of diphenylacetylene (DPA) in methylcyclohexane and acetonitrile as well as the rocking mode of methylcyclohexane (A H) at 547 cm À1 in isotropic liquids, liquid ordered phases, and solid matrices as a function of temperature have been recorded in the range 293±77 K. We have found that DPA±methylcyclohexane system exhibits isotropic liquid±anisotropically aligned liquid phase transition at 258 K and liquid±solid transition at 150 K. Mechanisms of vibrational relaxation and band broadening around 258 and 150 K transitions have been discussed. We have found that DPA molecules modify signi®cantly reorientation order of the host solvent molecules in the phase below 258 K that strongly deviates from isotropic alignment observed in the liquid phase above 258 K. This anisotropic alignment may come from liquid crystalline properties of DPA or liquid±solid interface interactions between methylcyclohexane molecules adsorbed on surfaces of DPA crystals.
Spectrochimica Acta Part A: Molecular Spectroscopy, 1987
Raman spectra of cis and tram isomers of 1,2-, 1,3-and 1,4dimethylcyclohexane have been recorded in the liquid phase at pressures up to 11 kbar and temperatures ranging from-80 to 120°C. Large relative integrated intensity changes (< 30% in some cases) were observed for all six fluids as both temperature and pressure were varied. These. changes cannot be explained solely by invoking temperature and pressure induced shifts in conformer populations. In the optical skeletal regions both increasing pressure and decreasing temperature suppress the intensity arising from symmetrical modes which involve significant volume changes. The C-H stretching regions behave differently in that increasing pressure and increasing temperature suppress the intensity arising from symmetric modes relative to that arising from antisymmetric modes. These observations suggest that the relative intrinsic scattering activities of vibrational modes are not independent of environment but are a function of both density and temperature. An explanation is offered which relates the relative intensity change as a function of density to the volume change associated with the vibration.
Pressure-induced dynamics in solid n-alkanes as probed by optical spectroscopy
The Journal of Chemical Physics, 1998
The dependence of frequency, width, and area of spectral holes on pressure were measured at 1.6 K in the pressure range up to 2.5 MPa for dimethyl-s-tetrazine ͑DMST͒ doped n-hexane ͑Shpol'skii system͒, and as reference systems, for DMST-doped durene ͑''hard'' molecular crystal͒ and ethanol:methanol glass. For the Shpol'skii system, in addition the inhomogenous fluorescence spectra were measured for normal and high ͑200 MPa͒ pressures. The main observations were the following: ͑i͒ spectral holes in the Shpol'skii system exhibit very large pressure-induced broadening ͑up to 65 GHz/MPa͒ depending essentially on the prehistory ͑freezing pressure͒ and exceeding the corresponding values for durene ͑by far͒ and glass; ͑ii͒ spectral holes in the Shpol'skii system exhibit strong, and to a large extent, reversible, area reduction with applied pressure; and ͑iii͒ the inhomogeneous fluorescence lines show quite a moderate ͑as compared to holes͒ pressure broadening of about several GHz/MPa. The results for the Shpol'skii system are shown to be inconsistent with existing theories. They are qualitatively explained by pressure-induced dynamics of vacancy defects in the frozen n-alkanes.
Crystals, 2018
Single-crystal samples of the semi-organic compounds mono-L-alaninium nitrate and monoglycine nitrate have been studied by Raman spectroscopy in a diamond-anvil cell up to 5.5 GPa, in order to observe the behavior of the deformation mode of NH 3 units. It was observed for these semi-organic crystals that increasing pressure produces a decrease in the wavenumber of the band associated with the deformation vibration, differently from most of the modes. Comparatively, mono-L-alaninium has a higher dν/dP than monoglycine nitrate, for the band associated with the deformation vibration. The anomalous behavior is explained in terms of the effect of high pressure in the short and linear intermolecular hydrogen bonds.
Chemical Physics, 1999
Ž. Ž. Raman spectra of the n C[C stretching mode of phenylacetylene PA dissolved in different solvents: methylcyclohexs ane, acetonitrile and benzene in frozen matrices at 77 K as a function of concentration have been recorded and compared with the spectra in the liquid phase. The optical measurements were complemented by the differential scanning calorimetry Ž. DSC scans. The results reveal some dramatic changes with solvent and concentration and are of potential relevance both to fundamental condensed phase modelling and to liquid crystal technology. We have discussed the origin of the splitting Ž. Ž. observed for the n C[C stretching mode of phenylacetylene PA and we have found that H-bond interactions are s responsible for the observed substructure in the vibrational spectra. We have found a glass-like transition at 183 K and two melting-like transitions at 200 and 218 K for PA in acetonitrile. In methylcyclohexane a melting transition starts at 120 K, and does not change in PA solution in contrast to PA in acetonitrile. The DSC scan for PA in methylcyclohexane shows additional phase transition at about 220 K.
… Acta Part A: Molecular …, 2005
In situ Raman spectroscopic measurements of water in the region of OH vibration were conducted up to 0.4 GPa at 23 and 52 • C. The frequencies of the decomposed OH stretching bands initially decreased with increasing pressure, reached a minimum at 0.15 GPa and increased up to 0.3 GPa and then decreased, which corresponds to the variations of the strength of hydrogen bonding. This variation was observed at 23 • C, but not at 52 • C, which suggests a change in pressure dependence on the hydrogen bond interaction between these two temperatures. Based on the equilibration model between hydrogen-bonded and nonhydrogen-bonded molecules, the present experimental results indicate that the pressure variation of the viscosity depends on the ratio of hydrogen-bonded molecules, rather than the strength of hydrogen bonding between molecules.
High pressure spectroscopic studies of hydrazine (N2H4)
Journal of Physics: Conference Series, 2014
Pressure-induced changes (up to 20 GPa) to the structure and bonding in hydrazine (N 2 H 4) have been investigated using diamond anvil cell (DAC) with in situ Raman spectroscopy. Liquid hydrazine solidifies at 0.3 GPa into a crystalline phase and its structure was established using synchrotron x-ray diffraction (XRD) measurements. The high pressure phase is monoclinic (P2 1) with a remarkable correspondence to the low-T monoclinic structure that is also seen in the similar Raman spectral features. With increasing pressure, the modifications to N-H … N hydrogen bonding is observed with emergence of new contacts beyond 5 GPa as well as appearance of new lattice modes. This is accompanied by small changes in the pressure dependency (dν/dP) of frequencies. Based on these observations, we conclude a sluggish phase transition in the 5-7 GPa range accompanied by selective strengthening and restructuring of hydrogen bonding network. Inelastic Neutron Scattering (INS) measurements performed in the 10-250 K range indicates that the order-disorder phase transition (observed in thin films at 175-80 K) driven by conformational changes is not observed in a bulk sample.
Two-dimensional Raman spectroscopy of vibrational interactions in liquids
1997
Two-dimensional fifth-order Raman spectroscopy has the ability to probe nonlinear interactions between well defined vibrational motions in liquids. It can reveal the nonlinear dependence of the molecular polarizability on vibrational coordinates, intermolecular interaction-induced effects, and anharmonic couplings between modes. We use this technique to probe these interactions at an intramolecular level in liquid CCl4 and CHCl3, and at an intermolecular level in a mixture of these two liquids.[S0031-9007 (97) 04158-6]
Effect of pressure on the Raman spectra of methanol-ethanol-water mixture at room temperature
Journal of Raman Spectroscopy, 2005
We measured Raman spectra for liquid methanol, ethanol, water and their mixture under ambient conditions. We also measured these spectra for wavenumbers in the range 1400-1600 cm −1 for methanol-ethanol (4 : 1) and methanol-ethanol-water (16 : 3 : 1) mixtures as functions of pressure up to 62 kbar at room temperature. We present results for the wavenumber, linewidth and relative intensity of the prominent bands as functions of pressure. These results should be useful for understanding the pressure (hydrostatic) dependence of the Raman spectra of solids.