Intermolecular Vibration Energy Transfer Process in Two CL-20-Based Cocrystals Theoretically Revealed by Two-Dimensional Infrared Spectra

Abstract

Inspired by the recent cocrystallization and theory of energetic materials, we theoretically investigated the intermolecular vibrational energy transfer process and the non-covalent intermolecular interactions between explosive compounds. The intermolecular interactions between 2,4,6-trinitrotoluene (TNT) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and between 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) and CL-20 were studied using calculated two-dimensional infrared (2D IR) spectra and the independent gradient model based on the Hirshfeld partition (IGMH) method, respectively. Based on the comparison of the theoretical infrared spectra and optimized geometries with experimental results, the theoretical models can effectively reproduce the experimental geometries. By analyzing cross-peaks in the 2D IR spectra of TNT/CL-20, the intermolecular vibrational energy transfer process between TNT and CL-20 was calculated, and the conclusion was made that the vibrational energy transfer process between CL-20 and TNTII (TNTIII) is relatively slower than between CL-20 and TNTI. As the vibration energy transfer is the bridge of the intermolecular interactions, the weak intermolecular interactions were visualized using the IGMH method, and the results demonstrate that the intermolecular non-covalent interactions of TNT/CL-20 include van der Waals (vdW) interactions and hydrogen bonds, while the intermolecular non-covalent interactions of HMX/CL-20 are mainly comprised of vdW interactions. Further, we determined that the intermolecular interaction can stabilize the trigger bond in TNT/CL-20 and HMX/CL-20 based on Mayer bond order density, and stronger intermolecular interactions generally indicate lower impact sensitivity of energetic materials. We believe that the results obtained in this work are important for a better understanding of the cocrystal mechanism and its application in the field of energetic materials.

Direct observation of photoinduced sequential spin transition in a halogen-bonded hybrid system by complementary ultrafast optical and electron probes

“…Among various intermolecular interactions, the halogen bond is one of the strongest interactions, with less than the sum of van der Waals (vdW) radii (3.78 Å). Because the VET process has been reported to be related to the strength of the intermolecular interactions 47 , 48 , the halogen bond is likely to be one of the prime pathways for VET from the photoexcited [Fe(Iqsal) 2 ] + cations to their nearest-neighbor [Ni(dmit) 2 ] − anions. In Fig.…”

Infrared spectra and electronic structural changes of DNTF under high pressure: experimental and theoretical studies

“…In this study, we employed experimental IR spectra at high pressures to investigate the structure stability and electronic structure change of DNTF. Subsequently, first-principles calculations were performed to elucidate the variation of the IR spectra and vibrational characteristics under high pressures, such as the crystal structure variation, free volume in the DNTF crystal, 18 non-covalent weak interaction by using the independent gradient model based on Hirshfeld partition (IGMH), [19][20][21] and energy gap. 22,23 The in-depth study in this area aids in understanding the response of the DNTF crystal to high pressures, and further providing the support for the application of DNTF in weapons and warheads.…”