A Density Functional Theoretical Study Of The Spin Forbidden Reactivity Of The Activation Of NH₃and Circularly Catalyzed N₂O/CO Molecules By Lanthanides Transition Metal In The Gas-phase

Some experimental chemists have found that transition-metal cations M+havepeculiar activations to the N-H, N-O and C-O bonds of small organic/inorganiccompounds in the gas phase using an inductively-coupled plasma selected-ion flowtube （ICP/SIFT） tandem mass spectrometer during the past decade. Recently, theactivation of traditionally inertia bonds （such as N-H bond, N-O bond） is becomingmore attractive for its importance in industry and basic chemistry research. Howevertheoretical approaches to these reactions also indicated that often the reactants andproducts had ground states of different spin multiplicities, and the transformations ofspin multiplicities occurs frequently in thermal reactions. Namely, the reactions didnot obey “spin conservation law”. During the process of a chemical reaction, theability of the metal center to access these states and adapt to different bondingsituations may enable the system to find low-energy reaction pathways that would notbe accessible otherwise. Thus, a reaction possibly occurs on two or more potentialenergy surfaces （PESs）. Such a phenomenon is called "two-state/multi-state reactivity（TSR/MSR）".The gas phase reactions of the activation of NH₃and circularly catalyzedN₂O/CO molecules by Lanthanides Transition Metal, which was found to be aspin-forbidden process. In this thesis, based on B hme, Schwarz and Schroder’sexperimental results, the activation of N-H, N-O and C-O bonds of small inorganicmolecules （such as NH₃, N₂O,CO） by bare transition metal cation have beenexamined using density functional theory （DFT） and CCSD（T） methods withcorresponding basis sets to explore the principle of two-state reactivity reaction. TheGaussian03, Gamess, and NBO program package were performed in this thesis.The whole paper consists of four chapters. Chapter1mainly reviews theprogress and application of quantum chemistry as well as the development and thepresent situation of TSR/MSR. The second chapter simply introduced the theoreticalbackground of this thesis, mainly contained the potential energy surface, traditionstate theory, the natural bond orbital and spin-orbit coupling mechanism etc. Thecontents of two chapters are the basis and background of our studies and offered us with useful and reliable quantum methods.In Chapters3and4, the gas phase reactions of Ce+and La⁺with NH₃, N₂O, andCO have been studied carefully using B3LYP methods and the activation of N H,N O, and C O bonds have been emphasized. The involving potential energy surfacecrossing behaviors have been discussed in detail. Firstly, for the activation of inertmolecules, the geometries of all the reactants, intermediates, transition states andproducts on the potential energy surfaces （PESs） are accurately optimized, and striveto establish a more accurate potential energy surface, in order to ensure the precisionof the results. Secondly, Vibrational frequency calculations and intrinsic reactioncoordinate （IRC） methods were used to characterize the reaction path channels on twoPESs. Then, on the basis of the Hammond postulate, the crossing points （CPs）between states of different spin multiplicities has been selected by means of theprocedure used by Yoshizawa et al. For the sake of comparison, the mathematicalalgorithm to MECPs developed by Harvey et al. had also been employed. Finally, tofurther explore the characteristics of non-adiabatic dynamics, the effective spin-orbitcoupling （SOC） in the MECP region is calculated using the GAMESS programpackage, and the probability of hopping from one surface to the other in the vicinityof the crossing region is calculated by the Landau-Zener type model, which is toinvestigate the dynamics characteristics of intersystem crossing. The energeticallymore favorable channel was confirmed according to thermodynamic and dynamicdate.