Transient Grating Spectrum Of Predissociation In Niromethane And Notrobenzene

As fuel and explosives, energetic materials play the important role in themilitary and aerospace. The researchers have never stopped exploring decompositionof energetic materials decompose under different conditions. Decomposition ofenergetic materials is an ultrafast chemical processes, the reactions finish inpicoseconds, which makes the research of decomposition of energetic materials moredifficult, especially the initial decomposition. With the development of lasertechnology and the emergence of ultrashort pulse laser, the resulting ultrafastfour-wave mixing spectroscopy provides us a powerful method to study ultrafastphysical and chemical processes.In this thesis, pre-dissociation process of two typical energetic materials,nitromethane and nitrobenzene, is studied by transient grating spectroscopytechnology. First, we analyzed the feasibility for studying the dissociation processwith transient grating technology on the basis of theory of transient gratingtechnology and pre-dissociation processes. Secondly, we get time-resolved transientgrating spectroscopy of nitromethane and nitrobenzene with femtosecondtime-resolved transient grating experiments. Finally, through the contrast analysis ofRaman spectroscopy and transient grating spectroscopy, vibrational modes areidentified, and their pre-dissociation processes are confirmed by analysis of kineticinformation of vibrational modes.In the pre-dissociation of nitromethane, energy transfers from CH3stretchingvibration to CH3bending vibration, and then to the C-N symmetric stretching. It maylead to C-N bond cleavage, with vibration energy accumulates at C-N bond energysymmetric stretching vibration. This is the “Ladder mechanism” dissociation. Thenitrobenzene pre-dissociation is a "big bang mechanism ", the dissociation may occursat NO2symmetric stretching vibration, CCC triangular bending vibration of benzenering stretching vibration and CCC in-plane bending vibration. The main paths ofdissociation may be through NO2symmetric stretching vibration and bendingvibration CCC triangular bending vibration.This thesis applies the transient grating technique in the study pre-dissociationprocess, as well as provides a theoretical reference to nitromethane, nitrobenzene andother energetic materials.