Theoretical Study Of The Reaction Of First-row Transition-metal Ions (M～+) With CS₂ And OCS In 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, did not obey "spin conservation law". These reactions have been named two-state reactivity( TSR). Examples were the reduction of water by the early transition-metal cations Sc⁺ and V⁺, oxidations involving the cationic metal dioxides VO₂ and CrO₂⁺. However, the spin inversion itself was often neglected, and it had even been argued that "the notion of 'spin-forbidden' of organometallic reactions in the condensed phase was inappropriate", 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. It 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 TSR. Today, Chemists had become increasingly interested in TSR in the world. In this paper, we chose several typical reactions(Sc⁺, Ti⁺, Mn⁺, Cu⁺ and Zn⁺ with OCS and CS₂)which have been carefully studied using quantum methods, obtained some interesting results.In the paper, on the basis of the molecular orbital theory, the tradition transition state theory as well as quantum chemistry theory, the systems chose have been investigated using Density Functional (DFT) Methods and the coupled cluster CCSD(T) calculations. 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 orbit. The reaction mechanism has been argued deeply using these datum.The whole paper consists of five chapters. In chapter 1, the development and the current situation of quantum chemistry and two-state reactivity (TSR) are explained. In Chapter 2, simply introduced elementary theory, mainly contained tradition transition state theory, ab initio theory, density functional theory (DFT), the reaction surface, crossing rules of the potential energy surfaces, spin-orbit coupling mechanism and rules for intersystem crossing. The contents of the two chapters are the basis and background of our studies and offer us with useful and reliable quantum methods.In Chapter3 and 4, the reaction of Sc⁺, Ti⁺, Cu⁺ and Zn⁺ with CS₂, which are selected as a representative system of reactions of first-row transition-metal ions with CS₂. The reaction mechanism between M⁺(M=Sc, Ti, Cu, Zn) in ground state and excitated state and CS2 has been studied in theory. Our calculations were performed on both surfaces of [M, C, S₂]⁺. We have analyzed potential energy surfaces (PES) crossing scenario, and have found the CPs by means of single-point computations. And probability of PES crossing has been calculated. In Chapter 5, the reactivity of Mn⁺ toward CS₂ and OCS on both septet and quintet potential energy surfaces have been investigated. We have found the CPs by means of single-point computations as a function of the structural change along the IRC. In order to have a deep understanding of the spin inversion, we discuss the action of frontier molecular orbital for CP.