Low-Energy Electron Scattering Studies Of Some Molecules:Isomeric And Fluorine-Substituted Effects

The isomerization effect and the fluorine substitution effect have received great attention in physics,biology,chemistry,medicine,and pharmacy.Due to different structures,molecular properties may show great differences;on the other hand,the similarity of isomeric molecular structures will result in similarity of electron density distribution of conjugated systems and similarity of the same transition energy level.The substitution of fluorine for the hydrogen on the methyl group can increase or decrease the stability of the ?^* resonance state,and methylation can also significantly change the probability of the electron attachment dissociation(DEA)reaction.In this thesis,we take three molecules of methylformamide,acetamide,and trifluoroacetamide as the research objects,and use the ab initio R-matrix quantum scattering method to study the isomerization effect and fluorine substitution effect of these molecules.The purpose is to understand the influence of these effects on the elastic scattering cross section and shape resonance state of low energy electrons.In this paper,In the fixed core approximation,the static exchange(SE)model and the static exchange plus polarization(SEP)model are used to calculate the elastic scattering integral cross sections,momentum transfer cross sections and differential cross sections of low-energy electrons with methylformamide,acetamide and trifluoroacetamide by using R-matrix method.In the SE and SEP models,there are convex resonance peaks in the integral cross-sections,which come from the symmetry of A" and show the characteristics of a ?^* shape resonance state.We found the effect of isomerism on the resonance state: the?^* resonance state of acetamide is higher than the?^* resonance state of methylformamide.We also found that the substitution of fluorine for the hydrogen on the methyl group led to a decrease in the position and width of the resonance state,indicating that the substitution of fluorine for the hydrogen on the methyl group made the resonance state more stable.In order to understand the essential characteristics of these resonance states,based on the relationship between the virtual orbit energy and the resonance state,the semi-empirical method is used to calculate the resonance state energy,which is found to be in good agreement with the resonance state energy calculated by R-matrix method.We have also studied the differential cross sections of low-energy electron scattering for methylformamide,acetamide and trifluoroacetamide molecules.The results show that when the scattering angle becomes larger and larger,the differential cross section generally shows a sharp downward trend,and the isomerism effect is more obvious in the large-angle area with higher incident energy.In general,as the incident energy increases,the cross sections of acetamide and trifluoroacetamide gradually become consistent.As the angle increases,the cross-sections of acetamide and trifluoroacetamide gradually approach,and they almost overlap around 180°;under larger incident energy,the cross-sections of acetamide and trifluoroacetamide are significantly different at large angles.The others are almost the same.It shows that fluorine substitution has an effect on the differential cross section at large angles,but has no great effect at small and medium angles.This research mainly includes four parts.The first chapter introduces the significance of isomerization effect and methyl substitution effect,as well as the research significance and current situation of electron molecular scattering.The second chapter introduces the theoretical methods of scattering calculation,namely ab initio R-matrix method and semi-empirical method.The third chapter introduces the low-energy electron scattering of methylformamide,acetamide and trifluoroacetamide In chapter four,we summarize and give the conclusion.