Theoretical Study of FHeO—and Development of Multi-Level Electronic Structure Methods

• Main Authors: Hui-Ju Chen, 陳惠如
• Other Authors: none
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/05032708435861441627

碩士 === 國立中正大學 === 化學所 === 93 === This thesis consists of four chapters .The first is theoretical prdiction of noble-gas containing anions FHeO—, the second is dynamic study for ethyl formate syn elimination reaction , the third is improved multi-level electronic structure methods (MLSEn+d) for atomization energies and reaction energy barriers, the fourth is rate constant calculation for HHeF →He+ HF reactions by variational transition state theory. In chapter 1, the structures and energies of the noble-gas containing anions FHeO- have been calculated by high-level ab initio calculation. The FHeO- were found to be deep energy minima at the singlet electronic state and their energies are significantly lower than those at the triplet state. High dissociation energy barriers to He + OF- were also predicted. The unexpected stability of the FHeO- was due to the dramatic ion-induced O=Ng bond formation. The calculated results suggested possible experimental identification of the anionic species and even some related “ionic compounds” under cryogenic conditions. In chapter 2, the thermal elimination reaction has been studied by density functional theory (DFT) and ab initio method , we also use dual –level variational transition state theory to calculate the rate constant at 100-1000 K. The calculated results show that tunneling was found to dominate the reaction below 500 K, and compared to experimental values, the rate constant included tunneling(CVT/SCT) is very closed to experimental values. In chapter 3, We have improved our multi-level electronic structure methods MLSEn for calculating the atomization energies and reaction energy barriers for neutral systems by using improved correlation-consistent basis sets for second-row elements. The re-parameterization of the improved methods MLSEn+d was based on updated databases of 109 atomization energies, 38 hydrogen-transfer barrier heights, and 22 neutral reaction barrier heights from a recently developed database of non-hydrogen-transfer reactions. The improved methods perform very well on all three types of energies with mean unsigned errors of 0.70, 0.87, and 0.69 kcal/mol by the MLSE4+d method. In chapter 4, The rate constants for the gas-phase dissociation of HHeF through the bending coordinates have been calculated using the dual-level variational transition state theory with quantized reactant state tunneling (QRST) from 20 to 1000 K, Tunneling was found to dominate the reaction below 600 K, and the rate constants were found to be approximately temperature independent below 250 K. The barrier of HHeF dissionation to He +HF at CCSD(T)/ag-cc-pVQZ level is 7.8 kcal/mol, compared to HArF and HKrF, the barrier is low and then the rate constant is very fast. We think that that is the reason why can not find HHeF in experiment.