Quantum Chemistry Study On Different Isomers For Pt_n⁺/Pt_n^- (n=3-6) And Reaction Of Pt₂ With CH₄ On Singlet And Triplet Energy Surfaces

The catalytic characteristic of Pt_n clusters is of great importance for catalysis. A theoretical study on the influence of charges on electronic structure and catalytic activity of the clusters will give spark on understanding the mechanism of the catalytic reaction involving Pt_n clusters.In chapter 1, the basic concept and reserch development on clusters, as well as platinum clusters were summarized basis on a survey of the related literature. The development of quantum chemistry and its application was introduced briefly in Chapter 2, also the Hartree-Fock equation, density functional theory, pseudo basis set and Gaussian program package were introduced in this part.In Chapter 3, 15 kinds of density functional model chemistry were tested for Pt_<sup>-C^-H system, and PBE1PBE/LANl2DZ was confirmed to be most suitable for the system. Chapter 4 gives the results and discussions on different isomers of Pt_n⁺,Pt_n^-(n=3-6) at different electronic states. The catalytic mechanisms of the reaction of Pt₂ ⁺ CH₄ on singlet and triplet surfaces were studied at PBE1PBE/LANl2DZ level in chapter 5.The main conclusions are as following:1. A comparison of 15 density functional model chemistry (LSDA, B3LYP, B3P86, B3PW91, PBE1PBE in combination with Los Alamos ECP plus DZ for Pt and D95V for C, H, LANL2TZ for Pt and aug-cc-pVTZ for C, H, Stuttgart RSC 1997 ECP for Pt and aug-cc-pVTZ for C, H respectively) for Pt-C-H system shows PBE1PBE/LANL2DZ is the most suitable for the system.2. Different electronic structures of isomers of Pt_n⁺/Pt_n^- (n=3-6) studied at PBE1PBE/LANL2DZ show that the ground states of Pt₃⁺ is ⁴A₁, which is a regular triangle structure, ²B₂ with equicrural triangle structure is the ground state for Pt₃^-, ⁴A₁ with regular tetrahedron structure is the ground state for Pt₄⁺, the ground state of Pt₄^- is sextet with distorted tetrahedron structure, the ground states of Pt₅⁺ and Pt₅^- are ⁶B₁ with C_2V plannar structure and ⁶A distorted trigonalbiyramid respectively, the ground state of Pt₆⁺ is three dimension structure with C_2V point group, it's electronic state is ⁴A₁, while the ground state of Pt₆^- is not available in this work.3. The catalytic mechanisms of the reaction of Pt₂ ⁺ CH₄ on singlet and triplet surface were studied at PBE1PBE/LANL2DZ show that there are similar catalytic mechanisms of the reaction at singlet and triplet states: They both have relative low activation energy. The difference of the mechanisms cuased by eletronic states was analysed in spect of eletron transfer. Base on the reaction mechanism, it is speculated that the final products of Pt₂ ⁺ CH₄ on singlet energy surface is CH₂=CH₂, while it is CH₃CH₃ on triplet energy surfaces.