Time-dependent Quantum Dynamics Study For Reactions Between Hydrogen And Group IV Hydride

Molecular reaction dynamics is a branch of chemical reaction dynamics. Researchwith quantum theory on the rule of molecular chemical reaction is one of the mostimportant topics. In the past twenty years, with the great development of quantum scattingtheory and the enhancement of calculating capacity, it was possible to take full quantumcalculation on reactions with no more than four atoms. But in chemical and biologicalfields, reactions always deal with more than four atoms. So, to take accurate full quantumcalculations on such reactions, some models and dimension-reduced calculating methodshave been provided to reduce the calculation difficulty such as adiabatic approach, fixedgeometry approximations and mixed quantum-classical dynamics methods.In this thesis, a new reduced dimensionality method, semirigid vibrating rotortarget(SVRT) model, is introduced. In SVRT model polyatomic molecule whose speciallocomotion can be accurately treated as a regular non-symmetry rotor is dealt with as twodifferent rigid segments which both can vibrate one-dimensionally through the line of theircentroid. Since SVRT model can relatively deal with the special locomotion, it can exactlydemonstrate reaction system's steric dynamics effect, which is very crucial in moleculereaction. This model is adaptive to polyatomic molecule one of whose bond is relativelyweaker and which can be divided into two segments at the end of the reaction. For thepolyatomic molecule reaction system, 7 degrees of freedom are necessary to describe it andfor atom-polyatom molecule reaction system, only 4 degrees of freedom are enough.In this thesis, the dynamics of theH + SiH₄ →SiH₃ + H₂ ,H+GeH₄ →GeH₃ +H₂ reactionsare studied for the first time by using atom-polyatom SVRT model. There are three mainreasons for selecting such reactions: First, they are typical atom-polyatom reactions;Second, these systems is measurable in experiments, so the results of the study will be ofmuch reference value for experiment researches and for further study of more complicatedsystems; Third, researches onH +CH4 →CH3 + H2 reaction were taken fully in details withSVRT model. By studying the other two reactions between group IV hydride and hydrogen,then contrasting their reaction threshold energy, reaction probabilities, we can find theinner rules. The vertical contrast of these reactions can prove the credibility of SVRTmodel and the potential energy surface (PES). According to this theory, the reactive polyatomic molecule XH4 (X=Si,Ge)is regardedas a diatomic molecule H ? XH3, therefore the reaction system can be regarded as anatom-diatom reaction system, thus reducing the system to a four-dimensional scatteringsystem, and the 'diatomic'molecule H ? XH3 always keeps the C3V symmetry. In theprocess of calculation, the time-dependent wave packet method is used; the split-operatormethod is employed to propagate the wave packet. To avoid boundary reflection of wavefunction, an optical absorbing potential is used in the calculation process. This thesisadapts Garcia's PES got by ab initial calculation, and calculates the reaction probabilities,cross sections and rate constants of the two reactions. After comparing and analyzing the calculated results, we get the followingconclusions: First, each of the two reaction systems has observable reaction probabilitywhen it approaches the barrier, which indicates quantum tunnel effects exist obviously.Second, the behaving that vibrating exciting of target molecule H ? XH3 increases thereaction probability enormously while they decreases the threshold energy evidentlyillustrates that the molecule's vibrating energy makes great contribution to collisionreaction. Third, the different rotating states for the molecule have on the reactionprobability influences, including that the increase of molecules'vibrating energy makesgreat contribution to abstract reaction while it has little effects on the reaction thresholdand that the initial geometry orientation for the reaction molecule has important influenceon the reaction probability. Fourth, the total cross-section of each of the reaction systemsincreases with the enlargement of the translational energy while the rate constant enhanceswith the rising of the temperature. By comparing the three Group IV hydride(X=C, Si, Ge),their rate constants increase respectively, then it shows that their stability much weaker in...