氧+甲醇及氧+甲基聯胺反應動力學Quantum Chemistry/RRKM計算

Abstract

摘要

我們利用quantum chemistry/RRKM理論方法研究O(1D)與甲醇及甲基聯胺的碰撞反應。討論其可能產生的反應物、中間產物、過渡狀態、各種脫除反應後產物的結構，研究其可能發生的各種反應機制及路徑，進一步計算出各途徑的反應速率與各種產物之產率。在O(1D)+CH3OH的反應中，由實驗得知，激態氧原子會經由插入C-H、O-H鍵生成diol intermediate trans-CH2OHOH以及peroxide intermediate CH3OOH，其生成比例假設為1：1。活性的CH3OOH、trans-CH2OHOH在碰撞能量7.3 kcal/mol下，經由理論計算得知生成H、H2、CH3O、OH、H2CO、CH2OH及H2O之產率分別為1.19、0.56、21.24、31.32、13.93、10.08及17.29 %。經由速率常數可推得，CH3OOH是OH的主要來源，trans-CH2OHOH是H、H2O的主要來源。此外，17.29 %水的產率是不可忽略的。同時根據實驗的結果以及理論計算所得到的結果，我們可歸納O(1D)+CH3OH在7.3 kcal/mol的碰撞能下，不會進行第二階段分解反應。

關於O(1D)+CαH3NβHNδH2反應方面，假設O(1D)+CαH3NβHNδH2可形成CαH2OHNβHNδH2、CαH3ONβHNδH2、CαH3NβOHNδH2、CαH3NβHONδH2、CαH3NβHNδHOH 等5種中間物，其生成比例假設為3：1：1：1：2。經由理論計算得知生成主要碎片NH2、H2O、H2、CH2OHNNH、OH、CH3NHN及CH3NHNH之產率分別為4.89、29.6、6.47、6.47、6.57、20.2及5.33 ％，佔了總產量的79.53 %。另外還有一些產率較低的碎片如：CH2OHNH、CH2NNH2、CHNHNH2、CH3、CH3NNH、CH3NH、CH3NHO、NHOH、CH2NHNH、CH3NNH2及ONH2，總共佔了總產率的20.47 %。整體來看，H2O、H2與OH自由基產率與先前所做同系列的計算不同，日後激態氧原子與聯胺類化合物的碰撞反應，H2O、H2與OH自由基應列為重要的偵測分子。

O(1D)+C2H6反應之同位素取代部分，除C2D5ODC2D5+OD以外，其他途徑的反應速率常數及產率皆因D取代而呈下降趨勢。與O(1D)+C2H6產率分布比較可知，CD3、OD等產物會因為D取代而使產率有較大的改變，CD3較CH3下降約1/3，而OD較OH增加約4.44倍。此外，D2O比H2O產率自26.8 %下降至22.8 %，這些數據的準確性在未來將可與實驗結果相互印證。Abstract In this present thesis, we used Quantum chemistry / RRKM theory to examine the reactions of O(1D)+CH3OH and O(1D)+CH3NHNH2. Studies of the possible geometries of reactant, intermediates, transition states and various products, allow us to understand reaction mechanisms and paths. furthermore, rate constants and product branching ratios of reaction channels can be derived. In O(1D)+CH3OH reaction, experiments show that excited oxygen atom can insert into C-H and O-H bonds to form diol intermediate trans-CH2OHOH and peroxide intermediate CH3OOH, respectively. According to experimental results, we assume the amount of CH3OOH is the same with trans-CH2OHOH. Calculation of the O(1D)+CH3OH reaction gave branching ratio of 1.19, 0.56, 21.24, 31.32, 13.93, 10.08 and 17.29 % for H, H2, CH3O, OH, H2CO, CH2OH and H2O, respectively. CH3OOH is the major source of OH fragment, and trans-CH2OHOH is the major source of H and H2O fragments. In addition, theoretical calculation predicted that a significant amount of H2O, 17.29%, can be produced in this reaction.

For the O(1D)+CαH3NβHNδH2 reaction, five long-lived complexes, CαH2OHNβHNδH2, CαH3ONβHNδH2, CαH3NβOHNδH2, CαH3NβHONδH2 and CαH3NβHNδHOH are expected. Ratio of their amounts are assumed to be 3:1:1:1:2, respectively. The calculation gave percentages of 4.89, 29.6, 6.47, 6.47, 6.57, 20.2 and 5.33 ％. For the NH2, H2O, H2, CH2OHNNH, OH, CH3NHN and CH3NHNH, respectively, while the products like CH2OHNH, CH2NNH2, CHNHNH2, CH3, CH3NNH, CH3NH, CH3NHO, NHOH, CH2NHNH, CH3NNH2 and ONH2 present lower yield of insignificance. In contrast to previous studies, significant amounts of H2, H2O and OH were produced in the type of reactions between excited oxygen atom and hydrazine.

Finally, we examined the O(1D)+C2D6 reaction to examine isotope effect. Except for the reaction channel of C2D5OD(1D)C2D5+OD, all of the rate constants decrease due to the deuterium substitution. Comparing with O+C2H6 reaction, the product branching ratio of CD3 and OD change dramatically where production of CD3 dropped 30% while production of OD increase 4.4 times. Finally, their reaction produced 22.8 % of D2O, which is slighter less than 26.8 % of H2O produced in O(1D)+C2H6 reaction.