Shocked Energetic Molecular Materials: Chemical Reaction Initiation and Hot Spot Formation

A theoretical model is developed to describe multiphonon up-pumping of internal vibrations. The dominant mechanism for up-pumping is anharmonic coupling of excited phonon modes with low frequency molecular vibrations, termed doorway modes. Quantitative calculations were performed which show the extent and rate of multiphonon up-pumping caused by shock excitation. The time dependence of chemical reactivity behind the front is calculated using reaction rate laws for the decomposition of nitramine explosives. A mechanism for hot spot formation, based on defect induced local increases in anharmonic coupling, is discussed.