Fig. 1. Schematic diagram of terahertz time-domain spectrum system

Fig. 2. Terahertz absorption spectrum of CL-20 during heating process

Fig. 3. Variation of absorption intensity at 1.53 THz frequency position during heating process

Fig. 4. Terahertz absorption spectra of CL-20 during natural cooling

Fig. 5. DFT calculation results and experimental spectra. (a) ε-CL-20; (b) γ-CL-20

Fig. 6. Vibration modes of ε-CL-20 absorption peaks. (a) 0.99 THz; (b) 1.10 THz; (c) 1.31 THz

Fig. 7. Vibration modes of γ-CL-20 absorption peaks. (a) 0.91 THz; (b) 1.53 THz