Theoretical Study Of The Adiabatic And Non-adiabatic Dynamics For LiHX(X= H,Cl)Reaction Systems

The aim of molecular reaction dynamics is to understand the reaction mechanism and control the reaction process.In this thesis,a set of non-adiabatic potential energy surfaces(PESs)about the ground and first excited state of LiH2 system and an adiabatic PES of LiHCl were constructed.The reaction dynamics of Li(2p)+ H2(X1∑+g)→ H + LiH(X1∑+)and Li(2S)+HCl(X1∑+)→LiCl(X1∑+)+ H(2S)reaction are investigated using the time dependent wave packet method(TDWP)based on the two PESs.In addition,the reaction mechanism of the two reactions are analyzed in detail.The dissertation is mainly focused on the following three parts:(1)The global diabatic potential energy surfaces which are correlated with the ground state 12A’ and the excited state 22A’ of the Li(2p)+ H2 reaction are presented in this study.The multi-reference configuration interaction method and large basis sets(aug-cc-pVQZ for H atom and cc-pwCVQZ for Li atom)were employed in the ab initio single-point energy calculations.The diabatic potential energies were generated by the diabatization scheme based on transition dipole moment operators.The neural network method was utilized to fit the matrix elements of the diabatic energy surfaces,and the root mean square errors were extremely small(3.69 meV for V11d,5.34 meV for V22d and 5.06 meV for V12d).Based on this new analytical diabatic potential energy surfaces,time-dependent wave packet calculation was conducted to investigate the mechanism of the title reaction.At low collision energies,the product LiH molecule tends to forward scattering,while at high collision energies,the forward and backward scatterings exist simultaneously.(2)The non-adiabatic state-to-state dynamics of the Li(2p)+ H2 → LiH + H reaction has been studied using the time-dependent wave packet method,based on a set of diabatic potential energy surfaces recently developed by our group.Integral cross sections(ICSs)can be increase more than an order of magnitude by the vibrational excitation of H2,whereas the ICSs are barely affected by the rotational excitation of H2.Moreover,ICSs of the title reaction with vibrationally excited H2 decrease rapidly with increasing collision energy,which is a typical feature of non-threshold reaction.This phenomenon implies that the title reaction can transformed from an endothermic to an exothermic reaction by vibrational excitation of H2.With the increase of the collision energy,the sideways and backward scattered tendencies of LiH for the Li(2p)+ H2(v=0,j=0,1)→ LiH + H reactions are enhanced slightly,while the backward scattering tendency of LiH for the Li(2p)+ H2(v = 1,j = 0)→ LiH + H reaction becomes remarkably weakened.The state-to-state differential cross section of reaction with H2(v = 1,j-0)indicate that the forward scattering LiH molecule is comes from the collision with small total angular momentum and the backward scattering LiH molecule is comes form the collision with large angular momentum.(3)A new global potential energy surface(PES)for the ground state of LiHCl system is constructed based on high-quality ab initio energy points which are calculated by the multi-reference configuration interaction method with Davidson correction.The AVQZ and WCVQZ basis sets are employed for H atom and Li atom,respectively.To compensate the relativistic effects of heavy elements,the AWCVQZ-DK basis set is employed for Cl atom.The neural network method is used for fitting the PES,and the root mean square error of fitting is small(1.36 × 10-2 eV).The spectroscopic constfants of the diatoms of the new PES are in good agreement with experimental data.Moreover,the geometric characteristics of the transition state and the complex are examined in detail and compare with the previous theoretical values.To study the reaction dynamics of the Li(2S)+ HC1(X1∑+)→ LiCl(X1∑+)+ H(2S)reaction,quantum reactive scattering dynamics calculations based on collection reactant coordinate based wave packet method are conducted on the new PES.The results of the reaction probabilities indicate that a small barrier exists along the reaction path as observed from the PES.The integral cross section curves reveal that the product molecule LiCl is easily excited.In addition,the reaction is dominated by forward scattering,and similar pattern is observed from previous experiment.