Theoretical Studies On The Intermolecular Hydrogen Bonding Properties And Vibrational Energy Transfer Processes In Energetic Molecule Systems

Energetic molecule systems,consisted by a class of organic molecules with amounts of stored chemical energy,are widely used in many industry processes and military purposes as propellants,explosives and dynamical energy resources because they have explosive properties and are flammable.In the systems,the main objective is to improve applicational performance by using current advanced technology,especially,increasing exploding and insensitivity.However,it is still a huge challenge to achieve the objective due to lack of a clear understanding about the basic interaction characteristics and dynamic processes of energy transfer in energetic molecule systems.Therefore,we carried out the basic work to understand the intermolecular interaction characteristics and energy transfer process in the energetic molecule systems at the atomic level,and further promote the development of corresponding basic research and application prospects.First of all,it was noticed that the hydrogen bond?H-bonds?in energetic molecule systems can improve the detonation and low sensitivity simultaneously.However,there is still a lack of regular understanding about how H-bonding affects the properties of energetic materials.Therefore,3,6-dihydrazine-tetrazine?DHT?,a high-density energetic molecule with strong H-bond network,was selected to explore intermolecular interaction properties of different structure types.The results showed that the intermolecular H-bonds of planar structures were stronger than that of non-planar structures in DHT dimer.More importantly,energy decomposition analysis?EDA?showed that the H-bonds of DHT dimers had stronger covalence-like properties.In planar structures,the ratio of the orbital interaction between molecules to all attractive terms is close to twice that of the non-planar structures.And the covalence-like properties increase with the strength of the H-bond,which leads to increase of intermolecular interaction strength.In addition,molecular orbitals?MOs?analysis showed that H-bonds interaction led to delocalization of intermolecular electron,that is,there were intermolecular penetrating orbitals,which also reflected the covalence-like properties of H-bond in this system from the perspective of electronic structure.In this work,it is not only for the first time proposed that H-bonds have the covalence-like properties in energetic molecule systems,but also rationally explain the essential reason why H-bonds can promote materials to achieve insensitivity.Further,intermolecular energy transfer plays an important role in the preservation and application of energetic molecule systems.Theoretically,Molecular dynamics?MD?simulation can study the energy transfer process at the atomic level to effectively understand the chemical reaction mechanism.By tracking the MD,the molecular structure,energy,and electronic interactions of systems all can be monitored.Therefore,using first-principles MD simulations,the intermolecular energetic transfer of nitromethane dimer was studied by exciting high-frequency intrinsic vibration?C-H stretching vibration?.And through short-time Fourier transform,the relationship of vibrational energy transfer characteristics with time was obtained.In particular,the study found for the first time a way that intermolecular energy transfer was faster than intramolecular energy transfer,which leads to the interesting situation by exciting the intrinsic vibrational modes with the same phase of H atoms.The mechanism is considered to be caused by the change of dipole moment center from electrostatic potential analysis of donor's H atoms plane.In addition,exciting the C-H strength motion of isomer,it was found that the relative position of the two monomers was changed and evolved in the direction of energy decrease.At the same time,the high-frequency vibrational modes were transferred to intermolecular vibration mode of low-frequency(less than 100 cm^-1).These findings provide an important reference for regulating the energy transfer process in energetic molecule systems,and provide a theoretical basis for understanding the intermolecular vibrational energy transfer and reaction mechanism.In summary,the intermolecular H-bond properties and MD simulation of energy transfer processes were studied.These works are expected to provide a way of improving the application performance of energetic molecules and designing new green high-density energetic materials.They can further offer a theoretical reference for understanding the related reaction process and even controlling of energy transfer in the reaction.