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研究生： 鄧乃偉
Nai-Wei Teng
論文名稱： 氧原子與烷類分子反應之計算化學研究
Computational chemistry study of O + small alkane molecules
指導教授： 孫英傑
Sun, Ying-Chieh
學位類別： 碩士
Master
系所名稱： 化學系
Department of Chemistry
論文出版年： 2003
畢業學年度： 91
語文別： 中文
論文頁數： 105
中文關鍵詞： 烷類分子 、氧原子
英文關鍵詞： RRKM, ab initio
論文種類： 學術論文
相關次數： 點閱：204  下載：0 
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    • 我們利用ab initio/RRKM理論方法完成O + C3H8 、 O + CH3F在交叉分子束環境下碰撞 propane經真空紫外光照射分解以及O + C2H6的氘( D )同位素取代效應等理論計算，包括了可能進行之多重分解路徑、反應速率常數及產率等動力學研究。在O + C3H8反應中O(3P) 與 C3H8不反應，而O(1D)會經由插入C-H鍵機構生成正丙醇及異丙醇，而正、異丙醇的比例最可能是90/10及100/0，活性的丙醇分子經第一階段分解計算出H、H2、OH、CH3、C2H5及H2O之產率分別為0.5、0.6、8.5、34.3、36.8及19.4 %，理論結果與實驗H、H2、OH、CH3和C2H5分別為0、0、25、27和48 %趨勢相符，並對於為何在O + CH4及O + C2H6反應中 H、H2的產率與O + C3H8明顯不同作了合理的解釋。經由O(1D) + C3H8的拔取機構計算得知，反應最後生成的OH產物總數會有部分比例來自O(1D)對C3H8末端H的拔取機構路徑。此外，理論發現反應存在著實驗不易偵測到的H2O產物，是一不可忽略的副產物。由更深入的反應計算結果，我們可歸納出O + C3H8在實驗8 kcal/mol的碰撞能下，不會進行第二階段分解反應。關於O + CH3F部分，O(3P)與CH3F不發生反應，而O(1D)插入C-F鍵需要11.2 kcal/mol，若經C-H鍵插入生成CH2FOH則反應能障近似於零，經由理論計算出HF、H、H2、OH、F及H2O之產率分別為69.9、8.0、2.3、2.0、10.1及7.7 %，除了F因基底大小因素外，理論值與實驗HF、H、H2及OH為82、11、7及0 %有良好的一致性，而此反應中亦發現實驗所沒偵測到的H2O產物。另外，求得O + CH3F的第二階段分解速率常數可輔助第一階段產率值，使理論產率與實驗結果更符合。
    利用與前述同樣之ab initio/RRKM理論方法進行propane光分解計算，我們描述了詳細的第一、二階段分解位能面與速率常數值，但發現第一階段分解理論產率在部分路徑與實驗差異較大，在包含第二階段分解後亦是如此，故推測RRKM理論之假設並不適用於propane光分解一例。本篇的最後完成了O + C2H6多重路徑分解的氘同位素取代研究，除OH分解路徑外，整體反應速率均因氘取代呈現下降趨勢，而比較O + C2D6與O + C2H6在產率上最明顯的差異為OH ( OD )產物，此部分之理論結果將來可提供實驗數據作參考。

    In the present thesis, we report the calculated results of O + C3H8 and O + CH3F reactions in crossed molecular beam collision-free environment using ab initio/RRKM calculation. In addition, propane photodissociation and O + C2D6 reactions were examined as well. Calculated results of rate constants, product branching ratios, and mechanism of possible multiple decomposition are presented. In the O + C3H8 reaction, O(3P) is not reactive with C3H8 but O(1D) can insert into a C-H bond of C3H8 to produce the n-propanol or iso-propanol. Considering steric hindrance and only two hydrogen atoms on the geminal carbon, we assume that the ratios of forming n-propanol to i-propanol is either 90/10, or 100/0. With the assumption of 90/10 ratio, product branching ratios of primary decomposition of the activated propanol are 0.5, 0.6, 8.5, 34.3, 36.8, and 19.4% for the H, H2, OH, CH3, C2H5, and H2O formation channels, respectively. The calculated results are in good agreement with available experimental results of 0, 0, 25, 27, and 48% for the H, H2, OH, CH3, and C2H5 products above, respectively. Our calculated results support that H and H2 do not produce in experiment. In the calculation of O + C3H8 for abstraction mechanism, the calculated results showed that this mechanism can contribute formation of OH radical unnegligibly. Furthermore, the theoretical calculation predicts the this O + C3H8 reaction can product H2O product, which was not detected in experiment due to high background noise. To examine further, we carried out calculations for secondary decompositions with 8 kcal/mol collision energy. The calculated results showed that secondary decompositions do not contribute detected product significantly. For the O + CH3F reaction, the calculation gave the percentage of 69.9, 8.0, 2.3, 2.0, 10.1, and 7.7% for the HF, H, H2, OH, F, and H2O, respectively. The calculated results are in good agreement with experiment results of 82, 11, 7, and 0% for HF, H, H2, and OH products. Significant amount of H2O was seen in calculation as well. Also, investigation of the rate constant of secondary reactions for this O + CH3F reaction also showed that the secondary reactions do not contribute to product yield significantly.
    In addition to the above calculations, the same ab initio/RRKM theoretical method was employed to examine the photodissociation of propane. The calculations gave in detail the potential energy surface and rate constants of primary and secondary decompositions. But we find a difference between the theoretical and experimental branching ratios for some channels. Based on an argument described in text, we think that RRKM theory is not suitable to describe the photodissociation of propane. Finally, we also carried out calculation for the O + C2D6 to examine isotopic effect of O + C2H6 reaction. Except for the OH channel, all of the rate constants decrease due to the deuterium substitution effect. The present theoretical calculated results can be verified in future experiments.

    第一章、緒論…………………………………………...…………….………1 1-1、簡介……………………………………………………………….…1 1-2、研究目標………………………………………………………….…8 第二章、計算理論原理及方法………………………………….……….10 2-1、計算理論…………………………………………………………...10 2-1.1、密度泛函理論（Density functional theory, DFT）…………10 2-1.2、偶合叢集方法( Coupled Cluster Methods, CC )………….13 2-1.3、改良式G2高度準確能量方法（G2MP2 or G2M）………15 2-1.4、RRKM理論 （Rice-Ramsperger-Kassel-Marcus Theory）………...….16 2-1.5、變分RRKM理論 （Varitational RRKM Theory, VRRKMT）…………....……18 2-2、計算方法…………………………………………………………...19 2-2.1、ab initio計算………………………………………………....19 2-2.2、RRKM與VRRKM 計算…………………………………….20 第三章、計算結果與討論……………………………………..………….23 第一部份、氧+丙烷反應之動力學ab initio/RRKM計算…..….....23 A. O(1D) + C3H8生成正丙醇及異丙醇……………………………….23 B. 正、異丙醇第一階段分解反應…………………………………….24 C. 第一階段分解之反應速率與產率…………………………………27 D. 獨特的OH channel………………………………………………..30 E. H2O產物的發現……………………………………………………31 F. 反應物之異構化及O(3P) + C3H8………………………………….32 G. 第二階段分解反應…………………………………………………33 第二部份 氧+氟甲烷反應之動力學ab initio/RRKM計算..…….51 A. O(1D、3P) + CH3F的反應性………………………………………51 B. CH3F(1D)多重路徑分解、互變反應及反應速率常數……………..52 C. CH2FOH(1D)第一階段分解反應及產率…………………………..54 D. CH2FOH(1D)第二階段分解反應及速率常數計算………………..56 E. O + CH3F與O + CH4多重路徑分解反應之比較………………..59 F. O(1D) + CH3F與N(2D) + CH3F之比較…………………………..60 第三部份 丙烷光分解反應之動力學ab initio/RRKM計算....….73 A. Propane第一階段分解反應位能面……………………………….73 B. Propane第一階段分解反應速率及產率………………………….75 C. Propane第二階段分解反應……………………………………….76 D. ab initio/RRKM方法與光分解反應……………………………….78 第四部份 O+C2D6經C2D5OD(1D)分解反應之動力學ab initio/RRKM計算…………………………………………...89 A. C2H5OH(1D)與C2D5OD(1D)分解反應之異同…………………….89 B. D取代之C-C與C-O分解路徑……………………………………90 C. 理論產率之比較…………………………………………………....91 第四章、結論……………………………………………………….……....98 第五章、參考文獻……………………………..…………………….……101

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