The Study Of Water And Nitromethane Structures Under Shock Wave Effect By Stimulated Raman Scattering

Water is the source of life,and it is also an important solvent.Therefore,the study of the molecular structure of water has always been a frontier subject which has both theoretical implications and practical applications.However,due to the structural complexity and weak spectral signal,the study of water structure remains challenging,especially the behavior of the water molecules in the extreme environment.We studied the hydrogen bond network of water molecules under dynamic high-pressure by stimulated Raman scattering(SRS)technology;at the same time this technique was extended to study cross pumping phenomenon in nitromethane.The innovative results achieved were listed as followed:(1)355 nm pulsed laser with different energies was used to excite the SRS of bulk water and water surface,and 532 nm laser pulse was used to excite the SRS of hydrogen peroxide solution.We observed the following phenomena: with the increase of laser energy,the two peaks of OH stretching vibration showed different frequency shift behaviors;different from the results of bulk water,on water surface,the OH vibrational Raman peak corresponding to strong hydrogen bond shifted to lower wave number;the OH bending vibration peak shifted to higher wave number with the increase of laser energy accompanied by the increase of intensity of Raman peak.Analysis: Shock wave induced dynamic high-pressure promoted the formation of strong and weak hydrogen bonds in water which resulted in the two peak distribution of SRS spectra,and the different energy dependent behaviors between the two peaks were attributed to the different proportion of strong and weak hydrogen bonds.Moreover,compared to the inside water,hydrogen bonds of surface water were stronger.On the other hand,the bending vibration mode of OH coupled with excess electrons of laser induced plasma which resulted in the higher frequency shift.This research provided a new idea for further exploring the molecular structure of water under dynamic high-pressure environment.This experimental method could also be applied to study the behavior of other liquid matrix under dynamic high-pressure environment.(2)SRS of 4 kinds of halogen ions including fluorine,chlorine,bromine and iodine ions in aqueous solution were studied by 532 nm pulsed laser.We found that the spontaneous Raman spectra and the SRS spectra of halogen ions aqueous solution showed different characteristics,and in the SRS spectra,with the addition of fluorine and chlorine ions,the stretching vibration peak of OH bonds showed red shift while for bromine and iodine ions it showed blue shift.Analysis: with the generation of laser induced plasma,the charge transfer occurred between fluorine/chlorine ions and water molecules to form weaker hydrogen bonds,resulting in a red shift of the OH stretching vibration peak,however there was no charge transfer between bromide/iodine ions and water,only the polarization effect occurred which resulted in shorter and stronger hydrogen bonds,so the peak of OH stretching vibration exhibited blue shift.This result could deepen the understanding of the hydrogen bond structure between halogen ions and water molecules,and provided a theoretical basis for the related chemical reactions as well.(3)SRS of nitromethane with the implantation of fluorescent seeds was studied with532 nm laser pulse.We found cross pumping phenomenon between the C-N vibration and C-H vibration inside nitromethane molecules,meanwhile fluorescent seeds could selectively enhance one vibration modes to excite the other vibration mode,and when fluorescent dyes increased to a certain concentration,the output signal became weaker.Because the first-order Stokes radiation of C-N or C-H vibration falling in the gain range of amplified spontaneous emission of corresponding fluorescent seeds,thereby the selective enhancement of cross pumping occurred;with the increase of the concentration of fluorescent dyes,the absorption loss increased to lead to the decrease of enhancement effect.This result could promote the study of detonating mechanism of nitromethane explosives,and also provide an idea for the development of tunable Raman laser.