Chemical Dynamics Simulation Of Hyperthermal Collisions Of N₂ With A Perfluorinated Alkanethiolate Self-assembled Monolayer

As an important gas component in Low Earth Orbit（LEO）,N₂ particles have an important influence on the surface material of spacecraft,but the mechanism of interaction with the surface remains unclear.In this simulation,the perfluorinated self-assembled monolayer（F-SAM）was selected as the organic surface model,which collided with N₂ particles for chemical dynamics simulation,and the effects of collision energy,incident angle and rotational quantum number on the dynamic process will be analyzed.In this paper,the geometry of N₂ and CF₄ is optimized by the MP2/aug-cc-pVTZ method and basis set,and the energy correction is performed for geometry by the CCSD（T）/aug-cc-pVTZ method and base set.And the method and basis set of CCSD（T）/aug-cc-pVTZ are used to calculate the single point energy of different orientation and obtain the corresponding potential energy curve.Then the interaction potential energy function between N₂ and F-SAM is developed by Genetic Algorithm,and its accuracy is further verified.Finally,the accurate potential energy function is obtained.The results of trajectory simulation show that the reaction mechanism between N₂and F-SAM can be divided into direct scattering mechanism,trapping desorption mechanism and trapping mechanism.The capture mechanism has the highest reaction probability under three different collision energies,followed by the direct scattering mechanism.The incident angle has the strongest influence on the probability of reaction,and the reaction probability of the trapping mechanism decreases sharply as the angle increases.At the same time,the energy transferred to the surface is also significantly reduced,however,72%of the collision energy is transferred to the surface at an incident angle of 60°.And the energy transferred to the interior of N₂ has increased,and this result may be due to the increase of incident angle resulting in an increase in the rotational energy of N₂.The rotational quantum number has little effect on energy transfer and the possibility of reaction mechanism.Under all initial conditions,the collision energy is efficiently transferred into the surface and this result may result in the breaking of chemical bonds in the surface.An important phenomenon was found in the simulation,when N₂ is trapped by the surface,the maximum depth of collapse in the surface is mainly concentrated in the same interval,which may help to further understand the aerospace material erosion mechanism.