【作者】 王健；

【导师】 孙家钟； 丁益宏；

【作者基本信息】 吉林大学 ， 物理化学， 2007， 博士

【摘要】 本文利用量子化学计算方法对几类重要的自由基、离子反应机理进行了详细的理论研究,给出了反应物、中间体、过渡态和产物的结构和能量以及相应的反应势能面的信息,讨论了可能的反应通道和反应机理。本文结果可为星际化学与燃烧化学中重要的自由基-分子、自由基-自由基和离子-分子反应模型的建立奠定基础,并可为实验室合成以及在星际太空中探测新型分子提供理论依据和支持。主要的内容有:i)首次探讨了典型反应CCN+CH₄的自由基-分子反应过程,发现它遵循卡宾插入机理,是一个无势垒过程。这一结论表明最近的实验可能有误（认为是直接氢提取过程,反应很慢）。该反应是第一个无势垒的非原子、不含氢的自由基-甲烷反应,有望在燃烧和星际过程的氮循环中起着重要作用。我们进一步研究了类卡宾自由基CCN与其它σ体系NH₃、H₂O、HF、PH₃、H₂S和HCl及π体系C₂H₂的反应机理,提供了该自由基反应活泼性的进一步证据; ii)详细地研究了C₂F+H₂O的反应,并且讨论了另一水分子的加入对于“准直接”氢提取主反应通道的催化作用; iii)结合主方程理论,研究了CH₃+CH_3-nCl_n （n=1,2,3）和CH₃+CCl₂的反应,计算了反应的速率常数,并与实验结果进行了比较;iv)首次研究了一价含硅离子SiCN⁺/SiNC⁺与气相σ分子体系CH₄、NH₃、H₂O、HF和H2的反应机理。与等价电子C₂N⁺+H₂O反应的卡宾插入机理不同,该反应采取的是亲核加成机制。这一研究有助于理解目前已经探测到的SiCN/SiNC自由基在经辐射或碰撞电离后的消除过程。由于SiCN+/SiNC+与NH₃、H₂O和HF反应没有（或很小）能垒,这也为半导体材料的气相沉积和星际过程中新型含硅化学键的形成提供了新的途径。更多还原

【Abstract】 Reactions of radicals and ions play a significant role in diverse environments such as combustion flames, the interstellar medium （ISM）, and planetary atmospheres. In this thesis, quantum chemical investigation on the potential energy surfaces of a series of important radicals and ions withσ-bonded orπ-bonded molecules as well as radical-radical reactions have been carried. Important information of potential energy surfaces such as structures and energies of intermediate isomers and transition states, possible reaction channels, reaction mechanisms and major products are obtained. The results obtained in the present thesis may be helpful for further theoretical and experimental studies of these kinds of reactions. The main results are summarized as follows:1. A detailed theoretical investigation on the potential energy surfaces （PESs） at the CCSD（T）/6-311+G（2df,p）//B3LYP/6-311g（d,p）+ZPVE computational levels is reported for the reactions of CCN with a series ofσ-bonded molecules XHn andπ-bonded molecules C₂H₂. Firstly, the cyanomethylidyne （CCN） and the other reactant approach each other forming a complex 1. Subsequently, the carbenoid insertion is confirmed as the most favored entrance channel to form isomer 2. For the previous experimental study of CCN with C_nH_2n+2, a hydrogen-abstraction mechanism was suggested, which is not in agreement with our result. Fo（rX,n）=（C,4）, （N,3）, （O,2）, （P,3）, （S,2）, the main reaction pathways are as follow: R CCN+ H_nX→H_nX…CCN 1→H（n-1）XC（H）CN 2→P₁ H_n-2XC（H）CN+H R CCN+ H_nX→H_nX…CCN 1→H_n-1XC（H）CN 2→H_n-2XC（H）₂CN 3→P₁ H_n-2XC（H）CN+H So, only the product P₁ H_n-2XC（H）CN+H should be almost exclusively observed. In addition, the product C₂H₃CN has been detected in interstellar space and the isomers H₃P-CCN and H₂S-CCN are considered to be similar to the ylides in nature, being“ylide-like radicals”. For（X,n）=（F,1）, （Cl,1）, the main reaction routs can be expressed below: R CCN+ H_nX→H_nX…CCN 1→XC（H）CN 2（?）XC（H）NC 6+（M or hv） R CCN+ H_nX→H_nX…CCN 1→XC（H）CN 2（?）XC（H）NC 6→R The isomers XC（H）CN 2 and XC（H）NC 6 can be stabilized by collisions or radiation. Without such stabilization, 2 and 6 may well dissociate back to the reactant R CCN+HX. For the reaction of CCN with C₂H₂, the main reaction channels can be indicated: Path 1: R CCN+C₂H₂→HCC（H）CCN 1→c-C（H）C（H）C-CN 2→P₂ c-C（H）CC-CN+H Path 2: R CCN+C₂H₂→HCC（H）CCN 1→c-C（H）C（H）C-CN 2→CC（H）C（H）CN 5→HCCC（H）CN 4→P₄ l-3HCCCCN+H Path 3: R CCN+C₂H₂→HCC（H）CCN 1→c-C（H）C（H）C-CN 2→H₂CC（C）CN19→H₂CCCCN 3→P₄ l-3HCCCCN+H Path 4: R CCN+C₂H₂→HCC（H）CCN 1→c-C（H）C（H）C-CN 2→H₂CC（C）CN 19→H₂CCCCN 3→P₃ CCCCN+H₂ Formation of cyclic HC4N may be more competitive than that of linear HC4N due to the lower-energy and simpler pathway of P₂ c-C（H）CC-CN+H. Formation of CCCCN radical is the least competitive though P₃ CCCCN+H₂ is almost isoenergetic to P₂ c-C（H）CC-CN+H. The studied CCN reactions could be of combustion and astrophysical interest and could provide efficient routes to form novel cyanogen-containing molecules in interstellar space.2. A potential energy surface involving the main structures of the C₂F+H₂O reaction calculated at the CCSD（T）/6-311+G（2d,2p）//B3LYP/6-311G（d,p）+ZPVE level is carried out. The main results can be written: R C₂F+H₂O→H₂O…CCF 1→P5 HCCF+OH R C₂F+H₂O→HCC（OH）F 7→H₂CC（F）O 6→H₂FCCO 5→P₁ CH₂F+CO R C₂F+H₂O→HOCC（H）F 2→HCC（OH）F 7→H₂CC（F）O 6→H₂FCCO 5→P₁ CH₂F+CO R C₂F+H₂O→HOCC（H）F 2→HFCC（H）O 4→H₂FCCO 5→P₁ CH₂F+CO The most kinetically competitive channel is the quasi-direct hydrogen-abstraction route forming P5 HCCF+OH. The overall H-abstraction barriers （4.5, 4.7 and 4.2 kcal/mol） for the C₂F+H₂O reaction are comparable to the corresponding values （5.5, 3.7 and 5.7 kcal/mol） for the analogous C₂H+H₂O reaction. The much less product is P₁ CH₂F+CO via the addition-elimination process. Furthermore, addition of a second H₂O can catalyze the reaction with the H-abstraction barrier significantly reduced to a marginally zero value （0.5 kcal/mol）. This is also indicative of the potential relevance of the title reactions in the low-temperature atmospheric chemistry.3. Four chloride-related radical–radical reactions, i.e., CH₃+CH₃-nCln （n=1,2,3） and CH₃+CCl₂, are theoretically studied for the first time by means of the Gaussian-3//B3LYP potential energy surface survey combined with the master equation study over a wide range of temperatures and pressures. The main reaction routs can be depicted: Path 1: nR CH₃+CH_3-nCl_n→H₃C-C（H）3-nCln na→nP₁ H₂C=C（H）_3-nCl_n-1+HCl Path 2: nR CH₃+CH_3-nCl_n→H₃C-C（H）3-nCln na→[H₃C-C（H）_3-nCl_n-1…Cl n （only for n=2, 3） ]→nP₂ CH₃-C（H）3-nCln-1+Cl Path 3: 4R CH₃+CCl₂→H₃C-CCl₂ 4a→4P₁ H₂C=CCl₂+H. Path 4: 4R CH₃+CCl₂→H₃C-CCl₂ 4a→H₂C-C（H）Cl₂ 4b→[H₂C（Cl）-C（H）Cl 4c]→4P₂H₂C=C（H）Cl+Cl Path 5: 4R CH₃+CCl₂→H₃C-CCl₂ 4a→4P₃ H₂C=CCl+HCl Our calculated results show that the three CH₃+CH₃-nCln reactions can barrierlessly generate the former two kinetically allowed products P₁ H₂C=C（H）3-nCln-1+HCl and P₂ CH₃CH₃-nCln-1+Cl with the very high predominance of P₁ over P₂. For the CH₃ reaction with the biradical CCl₂, which inevitably takes place during the CH₃+CCl3 reaction and yet has never been studied experimentally or theoretically, H₂C=CCl₂+H and H₂C=C（H）Cl+Cl are predicted to be the respective major and minor products. The results are compared with the recent laser photolysis/photoionization mass spectroscopy study on the CH₃+CH₃-nCln （n=1,2,3） reactions. The predicted rate constants and product branching ratios of the CH₃+CCl₂ reaction await future experimental verification. 4. A detailed mechanistic study on the singlet potential energy surfaces at the CCSD（T）/6-311+G（2df,p）//B3LYP/6-311G（d,p） computational levels was reported for the reactions of SiCN+/SiNC⁺ with a series ofσ-bonded molecules HX （X=H, CH₃, F, NH₂）. In contrast to the carbene-featured analogous CCN+/CNC++H₂X （X=O,S） reactions, the title reaction SiCN+/SiNC⁺+H₂O are not associated with any competitive silylene-insertion characters. The main reaction channels are shown: Path R（X）: SiCN++HX→HX…SiCN+ 1→HX…SiNC⁺ 4→XSiNCH+ 6→P₁ SiX⁺+HCN Path R’（X）: SiNC⁺+HX→HX…SiNC⁺ 4→XSiNCH+ 6→P₁ SiX⁺+HCN The initial gas-phase condensation between SiCN+/SiNC⁺ and HX （except the non-ionic H₂） effectively forms the adduct HX…SiCN+/HX…SiNC⁺. The stability of the adduct increases with the electron donating ability of X. Interestingly, the same major product P₁ SiX⁺+HCN for both reactions SiCN+ and SiNC⁺ can be obtained via the process of–CN（?）NC interconversion. The product P₂ SiX⁺+HNC is minor one. Even at low temperatures, reactions with the electron donors NH₃, H₂O and HF can also proceed rapidly via no barrier. This suggests that such reactions may be useful in the synthesis of novel Si-X bonded species. However, the reactions of completely saturated CH4 and H₂ produce fragments only at high temperatures.更多还原