Constructions Of Potential Energy Surfaces And Quantum Dynamics Studies For X⁺+H₂(X=N,Be) Reaction Systems

Molecular reaction dynamics aims at studying the nature and microscopic mechanism of chemistry reactions on the atomic and molecular level.Theoretically,the precondition of studying molecular reaction dynamics is to construct a global potential energy surface(PES),and then the evolution equation of the nucleus on the PES is solved.The three-atom system is a benchmark system for the study of molecular reaction dynamics,in which the reactions of ions with hydrogen and its isotopes have important applications in astrophysics,hydrogen storage and ultracold chemistry among other fields.The N+(3P)+H2(X1?g+)?NH+(X2?)+H(2S)reaction is the first step in the synthesis of ammonia within interstellar clouds.Most of the previous dynamics calculations about this reaction system were based on simple statistical models,and the reaction mechanism has not been thoroughly studied.The nonadiabatic reaction of Be+(2P)+H2(X1?g+)?BeH+(X1?+)+H(2S)has been widely concerned in low temperature experimental researches,but there is no detailed dynamics study in theory.In this thesis,the adiabatic PES of the ground state NH2+and diabatic PES correlated with the lowest two electronic states of BeH2+ are constructed based on high-precision electronic structure calculations and neural network method.Dynamics mechanisms of the above two reactions and their isotope substitution reactions are studied by using quantum time-dependent wave packet(TDWP)method on the two PESs.This paper focuses on the following three parts:(1)A global and accurate PES of the ground state NH2+is constructed by combining numerous high-precision ab initio energy points with the permutation invariant polynomialneural network method.Utilizing this newly constructed PES,the TDWP calculations are performed on the reactions of N+(3P)+H2 and N+(3P)+D2 to study the microscopic mechanisms and dynamical isotope effects.There are extremely dense resonant structures on the reaction probability curves due to the dominance of deep potential well on the minimum energy path.Compared with the product NH+ molecule,the ND+ molecule can be populated at higher rovibrational states.The total differential cross sections(DCSs)present the angular distributions of products are forward-backward symmetric,which are consistent with long-lived complex-forming mechanism.Whereas the rovibrational state resolved DCSs show obvious non-statistical behaviors.(2)A global diabatic PES correlated with the lowest two adiabatic states of BeH2+ system is constructed by using neural network method.ab initio energy points are calculated utilizing the multi-reference configuration interaction method and AVQZ basis set,and the diabatic potential energy matrix is obtained from the transformation of single point energy based on the dipole moment operators.The newly constructed diabatic PES can reproduce the adiabatic energy,and the spectrum constants of the H2(X1?g+)and BeH+(X1?+)molecules are in good agreement with experimental data.On the new diabatic PES,the TDWP calculations are carried out to study the dynamics mechanism of the nonadiabatic Be+(2P)+H2(X1?g+)?BeH+(X1?+)+H(2S)reaction.The results of dynamics calculations indicate that the product BeH+ molecule is mainly populated at high vibrational states and tends to backward scattering due to the nonadiabatic transition between different electronic states.(3)Based on the recently constructed diabatic PES,detail dynamics studies on the nonadiabatic Be+(2P)+HD?BeH+/BeD++D/H reaction are performed employing quantum TDWP method.The shallow wells induced by avoided crossing on the surface can efficiently promote the formation of BeD+molecule,resulting in the BeD+/BeH+branching ratio has a large value at low collision energy.This reaction presents different dynamics behaviors between the two reaction channels.The BeH+and BeD+channels are dominated by high-J and low-J partial waves,respectively.The BeH+product is primarily distributed at low vibrational states,whereas there is an obvious population inversion of vibrational states on the BeD+product.The DCSs results indicate that the BeH+channel is dominated by direct reaction mechanism,while the formation of BeD+channel follows the complex-forming mechanism.