**Investigation of direct and indirect phonon-mediated bond excitation in
alpha-RDX**

B Kraczek and PW Chung, JOURNAL OF CHEMICAL PHYSICS, 138, 074505 (2013).

DOI: 10.1063/1.4790637

We evaluate whether lattice or internal phonons dominate the thermal
excitation of the N-N bonds in alpha-cyclotrimethylene trinitramine
(alpha-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 alpha-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 N-N
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
non-shock decomposition of alpha-RDX.
**http://dx.doi.org/10.1063/1.4790637**

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