Theoretical Prediction of Noble-Gas Molecules and Comparison of Different Theoretical Methods
| Autor: | Ren-jie Lin, 林仁傑 |
|---|---|
| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 In chapter one of this thesis, we used theoretical methods, such as MP2, CCSD(T), and MPW1PW91, MPW1B95, and B3LYP, with 6-31+G** aug-cc-pVnZ ( n = D, T ) and MG3S basis sets to predict the stability of the novel noble-gas compounds XNgY ( X = H, F; Ng = He, Ar, Kr ; Y = CnH, CnHn+1, CmH2m+1; n = 2, 4, 6 ; m = 1~4 ) which contain Ng-C bonds with the sp, sp2 and sp3 hybridization on the carbon atoms. In this study, the accuracies of the various methods were based on the comparison to the relative energies calculated by CCSD(T)/aug-cc-pVTZ//MPW1PW91/aug-cc-pVDZ level. The results of this study suggest that FNgCnH ( Ng = Ar, Kr ; n = 2, 4, 6 ), HKrCnH ( n = 2, 4 ), FNgCnHn+1 ( Ng = Ar, Kr ; n = 2,4 ), FArCmH2m+1 ( m = 2~4 ), and FKrCmH2m+1 ( n = 1~4) could be detected in noble-gas matrix. From the comparisons of theoretical methods, the MP2 theory overestimates the strengths of sp and sp2 chemical bonding. The errors of MP2 theory are about 10~20 kcal/mol. On the other hand, the hybrid DFT methods perform much better, and the errors are usually less than 5 kcal/mol. In conclusion, the three hybrid DFT methods are much accurate and efficient choice for predicting the stability of noble-gas molecules. In chapter two, we used hybrid density functional theory methods, such as MPW1PW91 and B3LYP, with the 6-31+G** and aug-cc-pVDZ basis sets to predict the stability of aromatic noble-gas molecules and the effects of different substituents on the aromatic rings. We found that the aromatic noble-gas molecules containing He and Ar are very unstable. The stability of the aromatic noble-gas molecules containing Kr and Xe are only limited by the linear dissociation pathway, because their bending barrier heights are very high. The calculated results suggested possible experimental identification of the aromatic molecules containing Kr and Xe under cryogenic conditions. On the aromatic rings, we used different functional groups and at various positions to seek the influences upon the stability of aromatic noble-gas molecules. There is only about 1 to 2 kcal/mol difference on the same substituent in different positions. We also found that electron donating groups increased the stability by about 1 to 2 kcal/mol. On the contrary, the electron withdrawing groups will decrease the stability by about 1 to 2 kcal/mol. Since there are numerous possible aromatic derivatives, the number of potentially stable aromatic noble-gas molecules is very large. In chapter 3, we used ab initio method to predict the stability of NgO(H2O)n clusters. The calculated results suggested that the unstable NgO bond can be strengthened by the presence of water molecules. The effects are quite pronounced on the singlet-state surface, and are as large as ~20 and ~40 kcal/mol for Ar(H2O)n and Kr(H2O)n respectively. However, we also discovered the presence of water clusters cannot avoid the intersystem crossing of the cluster to the repulsive triplet-state surface on which the Ng-O bonds would dissociate immediately. Thus, the calculated results suggest it would be very difficult to identify the NgO(H2O)n even under cryogenic conditions. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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