Theoretical Study About Isotope Effect Of Hydriding For Aluminum Oxide And Potential Energy Function Of FeH₂

The Density Functional Theory is one of the quantum mechanic methods to investigate many electrons systems. It is one of the effective tools to study the molecular structures and properties of condensed systems. It is the common method to discuss the electronic structure in many fields.Transition metal hydrides, such as FeH₂, play a valuable role in the process of hydrogenation and alkane activation as well as the spectrums for FeH₂ found in the stellar atmosphere in favor of the research on the stellar evolution. On the other hand, aluminium compounds, such as aluminum oxides Al₂O₃ and aluminium hydrides are widely used in chemical reactions and rocket propulsion technologies. Therefore, the research on the properties and applications about metal hydride and aluminium oxides as rare earth has attracted many concerns.The research works in this academic dissertation consist of two parts:one aspect is that the potential energy function of two or three atomic molecular system and their ionic molecular system, mainly including the potential energy functions and its analytical expessions of the six molecules or ionic molecules of AlO neutral molecule, ±1valence of the cation and anion, ±2 valence of the cation and anion and Fe H neutral molecule.The analytical potential energy functions of FeH₂ triatomic molecule which are deduced by means of many body expansion theory, reconstructed the potential energy surface of ground FeH₂ molecule are stated in the first part of the research.The second aspect is that the changes of entropy, enthalpy and Gibbs free energy in the process of chemical reaction between aluminium oxide Al₂O₃ and hydrogen M₂?M=H, D, T?with the product of Al₂O₃M3. The relationships between the balance pressure of M₂ and the temperature and the isotope effect in the process have also been discussed.The first part of the research can be dived to two distinct parts. First, the balanced geometric configuration of AlO neutron molecule, ±1 valence of the cation and anion, ±2valence of the cation and anion are comparatively studied in the methods of varieties quantum mechanics method of two density functional theory method, MP2, CCSD?T? and QCISD. The two density functional method B3LYP and BP86 have been used to study the potential energy functions of the five molecule and their ionic molecules. Three analytica fuctions of four-parameter Murrel-Sorbie functions, Z-W functions and eight-parameter Murrell-Sobie functions are used to fit the six potential energy functions and deduced the analytical potential energy functions of the five molecule and their ionic molecules. The fitted effect of the three functions has been comparative studied. The results show that the eight-parameter analytical Murrell-Sorbie function has excellent fitted effect both in “stable type” or “volcano type”potential energy functions, the four-parameter analytical Murrel-Sobie functions have excellent fitted effect in “stable type” potential energy functions, but has bad fitted effects in“volcano type” potential energy and the analytical Z-W function cannt be used to fitted the“stable type” potential energy functions, but it has good fitted effect in fitting the “volcano type” potential energy, it's fitted effects are worse than that of analytical eight-parameter Murrell-Sorbie functions.The second subdivision of the first part research is in use of the three methods?B3LYP,BP86 and B3LYP*? of density functional theory?DFT?, the sufficient tools to predict the geometric configuration of metal hydride ground state, have been employed to optimize the structure of molecule Fe H and FeH₂ in possible geometries and multiplicities based on6-311++g?d,p? level for searching the lowest energy structure. The B3LYP method is used to predicte the harmonic frequencies and geometric parameters of the ground state of FeH₂, the results show that they are in good accordance with the experimental data. And their electronic states of ground states were Fe H?⁴?? and FeH₂?⁵A₁?, supposing the two molecule have three and four unpaired electrons with the spin polarization effect and they are paramagnetic substances, respectively and the stable structure of molecule FeH₂ was of C_2v symmetry. The Murrell-Sorbie potential energy function, the sufficient analytical potential function form for biatomic molecule, with 4 parameters of molecules Fe H has been derived from the least square method. Their spectra data and force constants have been deduced according to the results. The analytical potential energy function of FeH₂ has also been obtained from the many-body expansion theory. The many-body expansion theory supposed the analytical potential function of triatom molecule of the single value potential surface can be consisted of three parts with single body terms, two body terms and three body terms. The deduced analytical FeH₂ analytical functions in this paper predicted the global minimum stable structure of quintet FeH₂ with a 4.68 e V depth potential trap and other higher energy stable and saddle structure successfully. This potential function predicted the balance ground structure and second derivative force constants of this molecule. According to FeH₂ potential function, when FeH₂(C_2v) was formed from H and Fe H, a potential trap with the depth of 4.68 e V exited and the complex molecule of H-Fe-H was easily formed. The reaction of Fe+H₂?HFe H was exothermic and ?H =-0.08305 e V.The second part of the research is that the isotope effect in the process of the chemical reaction of Al₂O₃+3/2H₂?Al₂O₃H₃. In this part, the lower energy structures of Al₂O₃H₃ molecular clusters are optimized through DFT/B3 LYP connection with 6-311g++?d,p? all electrons basis set. It is found that the ground state configuration of Al₂O₃H₃ has' 1A electronic state and Cs symmetry. Based on the research for energy, heat capacity at constant volume,entropy of Al₂O₃M₃ and M₂?M=H,D,T?, hydrogen isotope effects of the reactions between Al₂O₃ and hydrogen?deuterium or tritium? gas are studied under the solid electron-vibration approximation method. In addition, the changes of enthalpy, entropy and Gibbs free energy and the relation between equilibrium pressures and temperatures have been presented. The investigation predicts that hydrogen can be displaced by deuterium and deuterium can be displaced by tritium in the reactions between Al₂O₃ and M₂ with the productions of solid Al₂O₃M₃?M=H,D,T?. This displacement sequence is opposite to metallic isotope e.g. titanium,however these displacement effects are so weak that they are approaching to disappearing with the temperature increasing.