3-Phonon Scattering Pathways for Vibrational Energy Up-pumping in Crystalline RDX

Up-pumping of shock energy to intramolecular vibrational modes may lead to breaking of critical bonds and phenomenon resulting in initiation in energetics. In this work, Fermi’s Golden Rule based 3-phonon scattering model is used over 216 kpoints throughout the Brillouin zone to investigate ~12 billion pathways for vibrational energy up-pumping in crystalline RDX [1]. On average, modes with frequencies up to 102 cm^-1 have the highest scattering rates and redistribute over 99% of the vibrational energy to other low frequency modes up to 102 cm^-1 within 0.16 ps. These low frequency modes transfer less than 0.5% of their vibrational energy directly to the NN stretching modes. The mid-frequency modes from 102 to 1331 cm^-1 further up-pump the energy to the NN stretching modes within 5.6 ps. The mid-frequency modes between 457 and 462 cm^-1 and between 831 and 1331 cm^-1 are the most critical for vibrational heating of the NN stretching modes and phenomena leading to initiation in energetics.

References

[1]G. Kumar, F. VanGessel, L. Munday and P. Chung, "3-Phonon Scattering Pathways for Vibrational Energy Transfer in Crystalline RDX," Journal of Physical Chemistry A, vol. 125, no. 35, pp. 7723-7734, 2021.