Zhanlong Li

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.

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.

Pressure-induced isostructural phase transition of a metal–organic framework Co2(4,4′-bpy)3(NO3)4·xH2O

Based on the 4,4′-bipyridine organic linker, metal–organic frameworks of Co2(4,4′-bpy)3(NO3)4·xH2O (CB-MOF) have been prepared. The pressure-dependent structure evolution of CB-MOF has been investigated up to 11 GPa. An isostructural phase transition was observed at about 6 GPa followed by negative compressibility along the b axis.

Influence of strong and weak hydrogen bonds in ices on stimulated Raman scattering

Stimulated Raman scattering (SRS) in liquid water and ice Ih using Nd:YAG laser is investigated. The spectrum of backward SRS (BSRS) in water is acquired. The spectrum shows an unexpected SRS peak at around 3453  cm(-1) besides the normal peak, which is similar to the spontaneous Raman spectrum of ice VII. The ice VII phase will be formed by laser-induced shock compression in liquid water. Simultaneously, unlike the spontaneous Raman spectrum, the pre-resonance SRS of ice Ih at around 3110 and 3210  cm(-1) is observed. The Raman peaks appeared in liquid water and ice Ih are attributed to the effect of strong and weak hydrogen bonds (H bonds), which should be ubiquitous in other ice phases.

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.

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.

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.

Study of hydrogen bonding in ethanol-water binary solutions by Raman spectroscopy

Raman spectra of ethanol-water binary solutions have been observed at room temperature and atmospheric pressure. We find that with increasing ethanol concentration, the symmetric and asymmetric OH stretching vibrational mode (3286 and 3434cm-1) of water are shifted to lower frequency and the weak shoulder peak at 3615cm-1 (free OH) disappears. These results indicate that ethanol strengthens hydrogen bonds in water. Simultaneously, our experiment shows that Raman shifts of ethanol reverses when the volume ratio of ethanol and the overall solution is 0.2, which demonstrates that ethanol-water structure undergoes a phase transition.

Phase-dominant pressure-induced planar molecular conformation of S-trioxane.

In situ high-pressure Raman spectra of S-trioxane have been measured up to 28 GPa. A first-order phase transition was detected at ~3 GPa from the splitting, newly existing and diminishing of the internal modes and from changes in the slope on plots of frequency versus pressure. The vibrational spectra and theoretical simulation indicate that the isolated molecule structure changes from puckered to very puckered structure at the first phase, while at the beginning of the second phase, S-trioxane goes back to its original puckered structure and loses its C3 axis; then, it changes to planar structure at about ~GPa and keeps its flat structure in the second phase up to the highest pressure studied. We believe that phase may be a dominant factor responsible for the pressure-induced planar molecular geometry, providing a reasonable explanation for the experimental observations.