Study Of Stimulated Raman Scattering And Hydrogen Bonding Network Structure Of Aqueous Solution

Water is one of the most important and abundant compounds on Earth,and its unique properties are associated with its complex network of hydrogen bonds.Raman spectroscopy of aqueous solutions can provide information about molecular vibrations,as well as study intermolecular interactions and hydrogen bond structures.Stimulated Raman scattering（SRS）is a third-order nonlinear effect with stimulated emission properties,often used as a complement to Raman spectroscopy to determine Raman peak locations and intermolecular interactions.While the two approaches are related in nature,there are clear differences between the two techniques.In this paper,hydrogen bonding network structure and optical frequency conversion in aqueous solutions of 1,2-propanediol（1,2-PD）and sodium sulfate aqueous solution were studied by spontaneous Raman scattering and SRS spectroscopy,and the pulse width compression behavior under laser-induced breakdown（LIB）in sodium sulfate aqueous solution was studied by stimulated Raman scattering.（1）In the study of aqueous solutions of 1,2-propanediol using spontaneous Raman scattering spectroscopy,it was found that the O-H telescopic vibration Raman band has the largest frequency shift when the volume fraction of 1,2-propanediol is0.4(V_1,2-PD=0.4).This indicates that the hydrogen bond network and association structure in the mixed solution change significantly as the volume fraction of1,2-propanediol increases.In the SRS spectroscopy of this solution,two new Raman peaks with wavenumbers at 3283 cm^-1 and 3319 cm^-1 appeared,based on the spectral behavior of methyl groups in 1,2-propanediol,which boils down to an“ice-like”structure.The results of quantum chemical calculations by density functional theory（DFT）method are also very consistent with the experimental conclusions.From the stimulated Raman scattering spectroscopy,it is found that when the volume fraction of 1,2-propanediol is 0.2,good dual-wavelength（631 nm and 650 nm）output can be produced,and changing the volume fraction of 1,2-propanediol can regulate the relative intensity of the dual-wavelength output.（2）Through the comparative experiment of SRS of pure water and sodium sulfate aqueous solution,it was found that the Raman peak of O-H stretching vibration moved from 3411 cm^-1 to 3447 cm^-1,which indicated that when sodium sulfate crystals were dissolved in water,the hydrogen bond structure between water molecules changed.For the SRS experiment of sodium sulfate aqueous solution:third-order Stokes and first-order anti-Stokes of S-O symmetric stretching vibration were detected under one sample cell condition;In the condition of dual cells,fifth-order Stokes and fourth-order anti-Stokes of S-O symmetric stretching vibration can be detected,and the phenomenon of crossing-pump was also found.The dual cell not only lowers the SRS threshold,but also enhances the four-wave mixing（FWM）process.And it was detected that the O-H first-order Stokes pulse width was compressed to 413 ps.SRS emission of aqueous sodium sulfate solution covered an ultrabroad wavelength ranging from 441 nm to 720 nm(a Raman shift ranging from-3859 cm^-1 to 4923 cm^-1).