Theoretical Study Of The Global Accurate Adiabatic And Diabatic Potential Energy Surfaces For The He And H₂ Reaction System

Hydrogen is the simplest element in the space of the universe,which is the main component of star formation.He and H₂are highly susceptible to collide in molecular clouds.The interactions with hydrogen and helium have significant applications in astrophysics and ultracold chemistry,which is very interesting for scientific research.The construction of accurate potential energy surfaces is an essential precondition for studying the kinetics of chemical reactions,from which we can obtain information in the reaction process,such as stable configurations,transition states,conical intersection avoided crossings part,and so on.Based on the importance of the potential energy surfaces,the global accurate potential energy surfaces have been constructed for these adiabatic and diabatic processes.To ensure the accuracy of the calculation results,the potential energies of He+H₂were constructed under the MOLPRO 2012 software package using the aug-cc-p V5Z basis sets,selected the MCSCF/MRCI high level method.The energy points in the range 0°-90°for the reactants and 0°-180°for the products were calculated,totally34848 ab initio energy points were calculated for each electronic state,and Jacobi coordinate was employed to express this system.To obtain accurate global energy surfaces,the B-spline fitting method was used.Since electrons would transfer near the interaction area,the Conical Intersection was optimized for the diabatic potential energy surfaces and the avoided crossing points were calculated for the adiabatic potential energy surfaces.Meanwhile,mixing angles were found,so the adiabatic potential energy surfaces could be transferred to diabatic potential energy surfaces for this reaction system.The one-dimensional potential energy surface for the H₂was analyzed in this study,and the vibration state energies were studied simultaneously.For the H₂molecule,13 vibrational states were found,and the equilibrium bond length of H₂is0.742?.All the results agreed with the former experimental and theoretical results.Thus all this proves that the global potential energy surfaces were accurate.In addition,the minimum global energy of the first excited state of the He+H₂reaction system was also obtained as 9.616 e V.The energy of the avoided crossing points was calculated,and the results were about 0.186 e V.The Conical Intersection was optimized in this study,and the geometry of this structure was similar to that of the avoided crossing point.The interaction was significantly stronger in this area,so the electrons would transfer between these two states.In the diabatic potential energy surfaces,the avoided crossing points for each angle were almost located in the same straight line,which means the diabatic potential energy surfaces were accurate.By analyzing these potential energy surfaces,the most reaction pathway was predicted,the reaction mechanism was refined.