Wenhui Fang

Raman spectra from Symmetric Hydrogen Bonds in Water by High-intensity Laser-induced Breakdown

Raman spectra of ice VII and X were investigated using strong plasma shockwave generated by laser-induced breakdown (LIB) in liquid water. Simultaneously, the occurrence of the hydrogen emission lines of 656 nm (Hα), 486 nm (Hβ), 434 nm (Hγ) and 410 nm (Hδ) was observed. At 5 × 1012 W/cm2 optical power density, the O-H symmetric stretching, translational and librational modes of ice VII and a single peak at 785 cm−1 appeared in the spectra. The band was assigned to the Raman-active O-O mode of the monomolecular phase, which was the symmetric hydrogen bond of cuprite ice X. The spectra indicated that ice VII and X structure were formed, as the trajectory of the strong plasma shockwave passes through the stable Pressure-Temperature range of ice VII and X. The shockwave temperature and pressure were calculated by the Grüneisen model.

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.

An insight into liquid water networks through hydrogen bonding halide anion: Stimulated Raman scattering

We have studied the interaction between water molecules and halide anions and acquired the influence of concentration by the spontaneous Raman spectrum. The results agreed well with the previous researches. To explore further, the stimulated Raman scattering of a halide–water binary solution is measured to study the nature of the hydrogen bonding between water molecules and halogen anions. Under the effect of laser-induced plasma, the OH stretching vibration spectra of aqueous solutions of halogen ions pretty exhibit different trend compared with that of spontaneous Raman spectrum. The frequency shifts of water OH vibration show different values and directions with adding different halide anions. The red shift of F−– and Cl−–water molecule clusters is due to the process of charge transfer, whereas the blue shift of Br−– and I−–water molecule cluster is due to polarization effect without charge transfer. The results demonstrate that F− and Cl− slightly weaken the hydrogen bond (HB), whereas Br− and I− enhance HB in the water cluster. The decrease of concentration of halogen ions aqueous solution can weaken the effect on the HB.

Stimulated Raman scattering from sulfur-II produced by laser decomposition of liquid carbon disulfide.

Stimulated Raman scattering (SRS) of sulfur-II (S-II) phase was investigated by laser decomposition of liquid carbon disulfide. As a matter of fact, above a threshold of the laser intensity, it is suggested that a strong shock wave is generated in the liquid carbon disulfide, which is decomposed owing to the induced high dynamic pressure and temperature. One bending mode E frequency at 289 cm(-1) and one symmetric stretching mode A1 frequency at 490 cm(-1) of S-II phase were observed. The SRS spectra indicated that S-II structure is formed by laser decomposition, as the strong shock wave generates the stable pressure-temperature range of S-II phase. The dynamic high-pressure and static-electric field generated by laser-induced breakdown results in the softening A1 mode becoming more hardened.