Zuowei Li

Study of high-pressure Raman intensity behavior of aromatic hydrocarbons: Benzene, biphenyl and naphthalene☆

Raman spectra of benzene, naphthalene and biphenyl have been taken up to a pressure of 13 GPa. The results for benzene and naphthalene indicate that the perturbation of inter-molecular π-π stacking effect on the Raman intensity is neglectable. For biphenyl, all the Raman peaks show intensity enhancement during the compression process, which indicates the planar intra-molecular aromatic conformation play an important role in the intensity increments of Raman bands. For three aromatic compounds, C-H stretching vibration bands located at about 3000 cm(-1) show intriguing intensity changes during compression account for the inter-molecular C-H⋯π interaction.

Stimulated Raman scattering of lattice translational modes in liquid heavy water.

A study was conducted on stimulated Raman scattering (SRS) when laser-induced plasma is formed in heavy water by focusing an intense picosecond pulsed Nd:YAG laser beam with wavelength 532 nm at room temperature. An unexpected 280 cm(-1) low frequency SRS line attributed to the lattice translational modes is observed. This SRS line and the internal-mode SRS lines indicate that the ice VII structure is formed in heavy water under the condition of laser-induced shockwave production.

Pre-resonance-stimulated Raman scattering for water bilayer structure on laser-induced plasma bubble surface.

Pre-resonance-stimulated Raman scattering (PSRS) from water molecules in the air/water interfacial regions was studied when the laser-induced plasma bubble was generated at the interfaces. A characteristically lower Raman shift of OH-stretching vibrational modes of water molecules at around 3000  cm(-1) (370 meV) was observed, in which the mechanisms were possibly attributed to the strong hydrogen bond in a well-ordered water bilayer structure that was formed on a laser-induced plasma bubble surface. Simultaneously, the PSRS of ice Ih at about 3100  cm(-1) was obtained, which also belonged to the strong hydrogen bond effect in ice Ih structure.

Estimating the pressure of laser-induced plasma shockwave by stimulated Raman shift of lattice translational modes

The current paper investigates stimulated Raman scattering (SRS) when laser-induced plasma is formed in heavy water by focusing an intense pulsed 532 nm Nd:YAG laser beam at room temperature. An unexpected low-frequency SRS line attributed to the lattice translational modes of ice-VII (D2O) is observed. The pressure of the plasma shockwave is estimated using low-frequency SRS line shift.

The Chlorophyll a Fluorescence Modulated by All-Trans-β-Carotene in the Process of Photosystem II

Modulating the chlorophyll a (Chl-a) fluorescence by all-trans-β-Carotene (β-Car) in the polarity and non-polarity solutions was investigated. The fluorescence intensity of Chl-a decreased as the concentration of β-Car increased. The excited electronic levels of Chl-a and β-Car became much closer owing to the solvent effect, which led to the electron transfer between both two molecules. A electron-separated pair Chl−·Chl+ that is not luminous was formed due to electron transfer. The solution of Chl-a and β-car in C3H6O was similar to the internal environment of chloroplast. We conclude that the polar solvent is good for the fluorescent modulation in photosystem II.

Carbon disulfide assisted polymerization of benzene.

The chemical transformation of benzene (C(6)H(6)) and carbon disulfide (CS(2)) binary solution under high pressure condition is investigated by means of Raman spectroscopy up to 6.8 GPa. On increasing the pressure, all the Raman bands of benzene decrease in intensity, whereas new broad bands start to be observed at 1520 and 1450 cm(-1), indicating that a highly cross-linked polymer is formed. The recovered sample is analyzed through Raman and FT-IR spectroscopy and is identified as a saturated hydrocarbon and element sulfur.

Anharmonic coupling between fundamental modes in tetramethylurea

In situ high pressure Raman spectra of tetramethylurea have been measured up to 25 GPa, liquid-solid and solid-solid phase transitions were detected at 0.2 GPa and 7.4 GPa, respectively. An unprecedented spectral phenomenon is the observation of a Fermi resonance between the fundamental modes. An exponential relationship between the intensity and the frequency difference was concluded. Pressure provides us a new way to study the correlation between Fermi resonance parameters.

Phase-transition induced changes in the electron-phonon coupling of all-trans-β-carotene.

The resonance Raman spectra of the fundamental, combination, and second harmonic modes around the C-C and C=C stretches of all-trans-β-carotene in 1,2-dichloroethane solution are obtained in the 323-83 K temperature range. The Raman scattering cross-section of the fundamentals in the liquid and solid phases generally increases as the temperature decreases, except for the liquid-solid phase transition, which exhibits a decreasing trend. The relative Raman intensities of the combination and harmonic modes of the CC bonds increase as the temperature decreases. The Raman bandwidths of the C=C bonds gradually become narrow but then appear a turning-point in the phase transition. The temperature-induced fundamental modes are analyzed using a coherent weakly damped electron-lattice vibration model and resonant Raman effects. The changes in the combination and harmonic modes are interpreted using the aforementioned model as well as the theory of electron-phonon interaction.

Hydrated-electron resonance enhancement O-H stretching vibration of water hexamer at air-water interface

Raman scattering of the O-H stretching vibration mode inside water, as well as near and at the air-water interface, was investigated by laser-induced breakdown (LIB). An intense and characteristic higher wavenumber Raman shift of the O-H vibration was observed at the air-water interface, which was attributed to the hydrated-electron resonance enhancement of the O-H stretching vibration mode of water hexamer. The hydrated electron in the water hexamer structure was formed by excess electrons injected into the gas-like phase with low hydrogen bond order under LIB. The electron-phonon coupled mechanism was discussed.

Temperature induced changes in resonance Raman spectra intensity of all-trans-β-carotene: changes in the fundamental, combination and overtone modes.

The resonance Raman spectra of the fundamental, combination and overtone modes around the CC and CC stretches of all-trans-β-carotene in 1,2-dichloroethane solution are obtained from the 293K to 83K temperature range. The results indicate that the intensity of the fundamentals in the liquid and solid phases generally increases as the temperature decreases, except for the liquid-solid phase transition, which exhibits a decreasing trend. The Raman intensities ratio between the fundamentals υ1 and υ2, combinations (overtones) and the fundamentals both increases with decreasing temperature. The Raman bandwidths of the CC bonds gradually become narrow as the temperature decreases. These varieties of relative intensity are analyzed using the coherent weakly damped electron-lattice vibration mode, the effective conjugation length mode as well as the theory of electron-phonon interaction in this work.