The Construction of Potential Energy Surfaces and Theoretical Study of Dynamics for XH2（X＝Au+,Na） Reaction System
Author:Wang Shu Fen
Supervisor:chen mao zuo
Molecular reaction dynamics is an important subject to understand the process and the mechanism of chemistry reaction,which is at the level of atom and molecule to understand the transition state of the reaction,differential reaction cross section(DCS)、inergral reaction cross section(ICS)、the results of the reaction probability et.al.In order to understand the reaction mechanism of the metals hydride,we used the multi-reference configuration interaction(MRCI)and neural network(NN)fitting method to build the ground state adiabatic potential energy surfaces(PESs)of Au+H2 and NaH2,the diabatic PESs of NaH2,which are correlated with the ground state and the first excited state.Based on these PESs,we analyze the reaction mechanism by the method of time-dependent quantum wave packet(TDWP).This paper contains the following three parts:(1)Based on 40352 high level energies,a new adiabatic PES of Au+H2 system is constructed by NN method;the root mean square error(RMSE)is 0.02 eV.In the ab initio calculation,the basis sets of H atom and Au+ ion are AVQZ and WCVQZ-PP respectively;the Davidson correction is used to obtain high-order correlation energy.In the fitting process,the NN structure has two hidden layers,and each layer containes 11 neurons.There is a potential well in the global minimum reaction path(MEP),and the reaction of Aud++H2→ H＋Au+H is endothermic.Based on the new PES.the TDWP studies for the Au++H2→H+Au+H reaction is carried out.In this reaction,when the total angular momentum quantum number equals 0,there is a threshold value of 2.63 eV and a large number of sharp and dense peaks on the reaction probabtility curve.Compared with Dorta-Urra PES,ICS of the new PES is closer to the expermential result;According to analyse the DCS.with the increase of collision energy,the forward scattering becomes more evident,the reaction is dominated by direct reaction mechanim.(2)A new PES for the ground state of NaH2 system is constructed based on 35730 ab initio energy points.Combining the basis sets of AVQZ and WCVQZ.the MRCI calculations with a Davidson correction are carried out to obtain the ab initio energy points.The NN method is used to fit the PES-and the RMSE is very small(6.39 meV).The spectroscopic constants of H2(X1∑g+)and NaH(X1∑+)obtained on the new NaH2 PES are good agreement with the experimental data.Compare the MEPs of the H(,S)+ NaH(X1∑+)→ Na(2S)+ H2(X1∑g+)reaction and H(2S)+LiH(X1∑＋)→Li(2S)+H2(X1∑g+)reaction,there is no barrier and potetntial well in the MEPs,and both reactions are exothermic,the exothermic energy is 2.784 eV and 2.235 eV,respectively.Based on the PESs of NaH2 system and L1H2 system,the TDWP method is applied to study the reaction dynamics.For the NaH2 system,the third vibrational excited state has the maximum ICS value,and the ground vibrational state has the minimum ICS value;However,for the LiH2 system,the state with the maximum ICS value is the second vibrational excited state,and the minimum ICS is the fourth vibrational excited state.The results of DCS show that the angular distribution of product molecule tends to the forward direction.(3)The Na(3p)+H2(X1∑g+)→NaH(X1∑＋)+H(2S)reaction pllays an important role in the field of diabatic reaction dynamics.A set of new diabatic PESs of the NaH2 system are structured,which include the diabatic coupling between the lowest two adiabatic states.The electronic structure calculations are performed on the MRCI level with the WCVQZ and AVQZ basis sets for Na and H atoms.32402 geometries are chosen to obtain the diabatic data by a unitary transformation based on the molecular property method.The diabatic matrix elements of Vd11,Vd22 and Vd12(Vd21)are fitted by artificial neural network.The spectroscopic constants of diatoms obtained from the new PESs are consistent with the experimental data.The topographical intersection characteristics of the Vd11 and Vd22 surfaces are discussed.There are barrier and potetntial]well in the MEP,considering the zero point energy effect,the endothermic energy is 0.63 eV.Based on the new PESs,the TDWP calculations are carried out to study the mechanism of the Na(3p)＋H2(X1∑g+)→NaH(X1∑＋)+H(2S)reaction in detail.The ICSs of vibrational excitation states keep growth at the collision energy below 1.5 eV.the ICS of the ground vibrational state increases and then decresed.The product molecule NaH tends to be forward scattering,with the increasing of the collision energies,the reaction is dominated by direct reaction mechanim.