T h i s is a preprint of a paper intended f o r pubhcalion i n a journal or proceedmgs. Since changes m a y be made before pubhcation, this preprint 1s made a v a l a b l e wlth the understanding that it w i l l not be clted or reproduced 1 without the p e r m i s s i o n of the author.

A survey of the literature has shown that there are eight possible initial unimolecular steps in the thermal decomposition of HMX. Of the eight steps, Arrhenius parameters have been estimated for four of them: reaction, log As (where As = A/s™1), E/(kcal/mol); N-N02 fission, 16.4, 46.2; homolytic C-N fission, 18, 60; five-center elimination of HONO, 10.8, >38; four-center elimination of HN02,10.8, >38. The depolymerization of HMX to 4CH2NN02 (a fifth possible step) was estimated to be 35.4 kcal/mol endothermic. The Arrhenius parameters are such thát N-N02 fission predominates at around 550 K. The estimated rate constant, 10™1 s~* at 500 K, is one power of ten less than previously measured rate constants for the overall decomposition.

A general model for the shock initiation of explosive reaction in chemical explosives is proposed. The model is based on the concepts of: (1) the kinetics of decomposition in which ions and free radicals produced by the shock wave shear forces initiate chain reactions that contribute to and accelerate the decomposition produced by the thermally activated molecules; (2) the formation of statistically random reaction sites whose number in a specific explosive is a direct function of the shock pressure as the shock transits the explosive; and (3) a critical‐ energy‐fluence requirement for initiation. This model appears to apply to explosive reaction in gases, liquids, and solids.

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The elucidation of the chemistry and physics of shock-induced chemical reactions and the initiation and detonation of chemical explosives has been slow and difficult. The processes involved often are not in thermal equilibrium, and they do not obey Arrhenius kinetics in the usual sense. Some calculations show a slow step in the transfer of shock energy to intramolecular vibrons from the lattice phonons that may limit reaction rates to around 107–109 s−1. Data and arguments are presented from Hugoniot and detonation studies that support a new concept of high-temperature kinetics. It is proposed that the averaged vibrational velocities of the atoms in condensed systems under the influence of high-velocity shock waves constrain the chemical reaction rates in the systems. This new concept is compared with alternative explanations and contrasted with Arrhenius processes.