Theoretical Study On The Structure,Properties And Dipole Bound States Of Molecular Anions

Molecular anions exist widely in interstellar media,astrochemistry,plasma and others.Due to the short-range attractive potential,the electronic characteristics of molecular anions are different from those of neutral molecules or positive ions.The research of the electronic states structure and dynamic processes of anions has become a very important topic in the field of atomic and molecular physics.Molecules can bound an extra electron by electron-dipole/quadrupole interaction to form non-covalent excited molecular anions,such as dipole bound states and quadrupole-Bound State anions.These special excited molecular anions play an important role in charge transfer process,DNA damage and verification of interstellar absorption spectra.Experimental and theoretical studies on the structure,properties and spectrum of molecular anions,especially the excited state and dynamic processes of molecular anions,which have become as a scientific research field that has attracted much attention in recent years.This paper starts from twelve polar alkaline metal diatomic molecules MX（MX=LiH,LiF,Li Cl,Na F,Na Cl,Na Br,KCl,Rb Cl,KBr,Rb I,KI,Cs I）.Based on accurate calculations of structures,spectroscopic constants and dipole moments of neutrals and anions ground-state,the dipole-bound states of these molecules and their energies are determined by continuously adding different diffusion functions basis sets with the EOM-EA-CCSD method.By comparing the computational results of the twelve molecules,the relationship between dipole-bound states and molecular properties is systematically analyzed.Based on the results of MX,a new strategy for judging the dipole bound state of molecular anion is proposed by calculating the dipole moment of anionic excited state using MRCI+Q method.The dipole bound states of some polar molecular anions are predicted by this strategy.In addition,the electron affinities of non-polar triatomic molecules（CO₂,OCS and CS₂）are calculated accurately.The main contents and results of this paper are as follows:（1）We studied the effects of different methods and basis sets focus on the dipole moment,electron affinity and spectroscopic constants of neutral and corresponding anion ground state of MX molecules.And we concluded that accurate geometric structure and spectroscopic constants information and analyzed the changes trend of structures and spectroscopic constants of different molecules.（2）Under the framework of EOM-EA-CCSD theory,by adding different layers of diffusion functions to the Correlation Consistent Basis Sets,and investigating the convergence of the electron binding energy of excited states within the different diffusion function basis sets,the energies of twelve MX molecule anions dipole bound states are determined.The analysis shows that there are at least twoσ-type dipole bound states in the anions with molecular dipole moment greater than 7 D and at least oneπ-type dipole bound state in the anions with molecular dipole moment greater than 10 D.Our calculation reproduces the experimental results of two dipole bound states of KI molecule,predicts anotherσtype dipole bound state,and gives the information of spectroscopic constants of dipole bound states.（3）We concluded that the dipole moment of DBS is in the range of dozens Debye to 100 Debye,while the larger dipole moment is a quasi-continuous state close to the ground state of neutral molecule,calculating and analyzing the DBS dipole moment of MX molecule anions.Based the results of MX,we propose a strategy to judge the molecular anion dipole bound states by calculating the dipole moment with the MRCI+Q method.We reproduced the experimental results of KI molecular anions DBS and the dipole bound states are successfully predicted within the different types of polar diatomic molecular anions and C_XN series molecular anions.（4）We investigated the effect of different basis sets,correction effect and zero-point energy on the adiabatic electron affinity for linear triatomic molecules CO₂,OCS,CS₂ base on the CCSD（T）and UCCSD（T）method and obtained the exact electron affinities of these molecules.