The coupling of inter- and intramolecular vibrations plays a critical role in initiating chemistry during the shock-to-detonation transition in energetic materials. Herein, we report on the subpicosecond to subnanosecond vibrational energy transfer (VET) dynamics of the solid energetic material 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) by using broadband, ultrafast infrared transient absorption spectroscopy. Experiments reveal VET occurring on three distinct time scales: subpicosecond, 5 ps, and 200 ps. The ultrafast appearance of signal at all probed modes in the mid-infrared suggests strong anharmonic coupling of all vibrations in the solid, whereas the long-lived evolution demonstrates that VET is incomplete, and thus thermal equilibrium is not attained, even on the 100 ps time scale. Density functional theory and classical molecular dynamics simulations provide valuable insights into the experimental observations, revealing compression-insensitive time scales for the initial VET dynamics of high-frequency vibrations and drastically extended relaxation times for low-frequency phonon modes under lattice compression. Mode selectivity of the longest dynamics suggests coupling of the N–N and axial NO₂ stretching modes with the long-lived, excited phonon bath.

中文翻译：

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1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) 薄膜中的模式选择性振动能量转移动力学

分子间和分子内振动的耦合在高能材料从冲击到爆炸的转变过程中引发化学反应中起着关键作用。在此，我们通过使用宽带超快红外瞬态吸收光谱报告了固体含能材料 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) 的亚皮秒到亚纳秒振动能量转移 (VET) 动力学。实验表明 VET 发生在三个不同的时间尺度上：亚皮秒、5 ps 和 200 ps。中红外所有探测模式的信号超快出现表明固体中所有振动的强非谐耦合，而长期演化表明 VET 是不完整的，因此即使在 100 ps 上也没有达到热平衡时间尺度。密度泛函理论和经典分子动力学模拟为实验观察提供了有价值的见解，揭示了高频振动的初始 VET 动力学的压缩不敏感时间尺度和晶格压缩下低频声子模式的弛豫时间大幅延长。最长动力学的模式选择性表明 N-N 和轴向 NO 的耦合_{2 种}拉伸模式与长寿命、激发声子浴。