Theoretical Study Of The Reactivity Of Transition Metal Ions With CO₂ And N₂O In The Gas Phase

Recently, theoretical approaches to gas-phase transition-metal chemistry indicated that often the reactants, possible intermediates, and products had ground states of different spin multiplicities. Namely, do not obey "spin conservation law". Although the necessity to explicitly consider surface hopping as a mechanistic step in organometallic chemistry was pointed out more than 10 years ago, the assumptions of either strict spin conservation or its complete neglect prevailed until 1994. This was in part due to difficulties in the appropriate theoretical descriptions of spin crossover in polyatomic metal compounds and, more importantly, the lack of unambiguous experimental examples for a violation of spin conservation along the reaction path, which provoked the necessity to tackle "two-state reactivity (TSR)". Today, Chemists had become increasingly interested in TSR in the world.In the paper, on the basis of the molecular orbital theory, the tradition transition state theory as well as quantum chemistry theory, the systems choosed have been investigated using Density Functional (DFT) Methods. The structures of the reagents, the reaction products and the transition states along the reaction paths have been obtained, then obtained the reaction surfaces, the spectrum datum, the thermodynamic datum as well as the information of orbitals. The reaction mechanism has been argued deeply using these data.The whole paper consists of six chapters. Chapter 1 describes the progeess and application of quantum chemistry as well as the development and the present situation of two-state reactivity (TSR). In Chapter 2, introduces elementary theory and quantum chemistry computation methods, which mainly contained the reaction surface, crossing rules of the potential energy surfaces, tradition transition state theory, spin-orbit coupling mechanism and rules for intersystem crossing. The contents of the two chapters were the basis and background of our studies and offer us with useful and reliable quantum methods.In Chapter 4, 5, 6, the reactions of Y⁺, Zr⁺, Nb⁺, La⁺, Hf, Ta⁺, W⁺ with CO₂, which are selected as a representative system of reactions of second-row and third-row early transition-metal ions with CO₂, have been studied carefully using UB3LYP methods. The activation of C-O bonds and ability of O capture by transition-metal ions have been emphasized. The involving potential energy surface crossing has been discussed detailedly. In Chapter 6, the reactivity of 4d transition-metal ions toward N₂O in two spin states has been investigated. We have analyzed potential energy surfaces (PES) crossing scenario, and have found the CPs by means of single'-point computations. In the study courses, Firstly, the formation and character of the reactant concomplexes have been discussed using the electronic charge transfer, the NBO analysis and the molecular orbital theory. Secondly, the - reaction path channels have been studied on two potential energy surfaces (PESs). Thirdly, the PES crossing dramatically affecting reaction efficiency and the reaction rate has been studied by means of the Hammond postulate and the intrinsic reaction coordinate (IRC) approach used by Yoshizawa et.al. and a series of crossing points (CPs) involving the structures and energy values have been located. Finally, in order to have a deep understanding of the spin inversion, we discuss the action of frontier molecular orbital for CP.