Investigation of Direct and Indirect Phonon-Mediated Bond Excitation in α-RDX

Report No. ARL-RP-471
Authors: Brent Kraczek; Peter Chung
Date/Pages: January 2014; 14 pages
Abstract: We evaluate whether lattice or internal phonons dominate the thermal excitation of the N–N bonds in α-cyclotrimethylene trinitramine (α-RDX) by computing the fractional contributions of phonon modes to the excitation of all atomic interactions. We derive a method to compute these contributions, which we call mode energy fractions, from the phonon eigenvectors and a splitting of the dynamical matrix. This enables identification of phonon modes that most strongly excite the N–N bonds that play a key role in molecular decomposition of α-RDX. Correlating these fractions with the mode populations and contributions to the specific heat and thermal conductivity, we analyze how thermal energy is distributed by phonons following a passing shock. Contrary to the common explanation that thermal energy is transferred to the NN bonds indirectly, by internal phonons, we find that lattice phonons dominate this thermal energy transfer, implying that energy flow follows a direct route. We also comment on implications of these results for nonshock decomposition of α-RDX.
Distribution: Approved for public release
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Last Update / Reviewed: January 1, 2014