Research On Raman Spectroscopy Of Liquid Nitromethane Under Single Shock Comprssions

The research on microscopic dynamic changes of energetic materials under shock-wave loading conditions has always been the research focus of the scholars all over the world, and it is also one of more challenging problems for the researchers to study these questions. Although people has made great advances in the field of the macroscopic properties and stability of energetic materials, the micro reaction mechanism and the shock initiation process of energetic materials under the conditions of high temperature and high pressure is poorly understood. Nitromethane is an organic material which has the simplest molecular structure, it can be used as the model for other nitro derivatives, and the dynamic problems of nitromethane under shock-compressed conditions have been always focused by most relevant researchers.The experiments in this thesis are performed in the experimental platform of a two-stage light gas gun, and Raman spectra of liquid nitromethane were online measured in single shock compression using the transient laser Raman spectroscopic system with high sensitivity. At ambient conditions, nitromethane has three strong vibration Raman peaks called as Raman characteristic peak:CN stretching vibration (917cm-1), NO2/CH3 stretching vibration/bending vibration (～1400cm-1), CH3 stretching vibration (2968cm-1); the information on molecular changes of nitromethane in liquid under shock can be obtained by monitoring the changes in the three Raman bands with increasing pressure. In this work, we firstly detected the Raman bands of liquid nitromethane at the shock pressure of 12.3 GPa, which is a major breakthrough in the field of researching the Raman spectra of liquid nitromethane under single-shock compression conditions. The experimental results show that, at the shock pressure between 7.9 GPa and 12.3 GPa, the Raman shifting of the CN and CH3 stretching modes increase monotonously with the increase of shock pressure, the magnitude of the shifting depends on the corresponding vibration mode; all Raman peaks show the broadening of peak width and the increase or decrease of peak intensity with increasing pressure; however, although changes in Raman peaks are observed, the results show no signs of chemical reactions occurred in the sample in this work. The results demonstrate the shock-induced reactions in liquid nitromethane did not occur at the high pressure range below 12.3 GPa, and its molecular structure still remains stable under this conditions, which solves the early argument about the shock-induced reactions of liquid nitromethane in single shock experiments. It can be deduced from the experimental results that the changes in molecular structure of liquid nitromethane may be determined by the combined effects of high pressure and high temperature in experiments of shock loading.