A nonequilibrium kinetic model of high-resolution vibrational energy transfer in RDX from selective IR excitation.

This article focuses on modeling nonequilibrium vibrational energy transfer (VET) in α-RDX, a molecular crystal, using a second quantization approach combined with anharmonic phonon scattering and the phonon Boltzmann transport equation (PBTE) based on Fermi’s golden rule. The model simulates mid-infrared pump–probe spectroscopy experiments, reproducing key experimental observations such as the prompt broad-spectrum phonon excitation and revealing distinct VET pathways, including rapid energy transfer among modes near the excitation frequency, overtone coupling between modes near 550 and 1150 cm⁻¹, and strong mediation by high-frequency C–H stretching modes above 2800 cm⁻¹. The study identifies significant coupling between N–N/N–O stretching modes and C–H modes, suggesting mode-selective vibrational activity relevant to chemical bond cleavage and initiation mechanisms in RDX decomposition. These findings provide detailed insights into phonon kinetics and energy transfer processes in molecular solids under external excitation, with implications for understanding sensitivity and initiation in energetic materials.