以交叉分子束技術及量子理論計算研究雙重態氮原子N(2D)與丙烯之反應動態學

Abstract

本論文利用交叉分子束技術研究雙重態氮原子N(2D)與丙烯(C3H6)之反應動態學。利用高電壓放電裝置產生氮原子與丙烯進行反應，反應碰撞能量約為5.3 kcal mol-1。反應產物利用可調能量之真空紫外光游離後，結合四極質譜儀作為偵測系統，取得反應產物之飛行時間譜(Time-of-flight spectra)。經由模擬反應產物之飛行時間譜，可得到在質心座標下反應產物之動能分佈以及角度分佈。並以Density functional theory與Coupled Cluster之理論計算方法模擬反應之位能面(Potential energy surface)幫助分析，解析反應動態過程。 雙重態氮原子與丙烯反應之實驗結果主要有三個反應通道，分別為C3H5N + H、C3H4N + 2H及C2H3N + CH3，經由動能分佈之最大動能及位能面推論反應產物結構主要為CH2CHNCH2 + H、CH3CHCN + 2H及c-CH2(N)CH + CH3。產物反應途徑主要為N(2D)加成至C3H6之π鍵上形成環狀之反應中間物，直接斷鍵形成產物或經過異構化才斷鍵形成產物。對照過去文獻N(2D)與乙烯(C2H4)之反應結果，僅有C2H3N + H之反應通道被觀測，產物C2H3N之角度分佈呈現偏向forward，而本實驗類似之反應通道C3H5N+H，產物C3H5N之角度分佈呈現偏向backward，顯示N(2D)與C3H6反應產生氫原子之反應途徑不同於N(2D)與C2H4之反應途徑。產物CH3CHCN角度分佈具有等向性(isotropic)，顯示來自於多步驟之異構化而產生，而過去文獻N(2D)與C2H4之反應並未報導C2H2N + 2H之產生。產物c-CH2(N)CH之角度分佈呈現偏向forward，顯示來自於一生命期較短之反應中間物。 交叉分子束儀器結合理論計算之反應位能面，提供了N(2D)與C3H6之反應資訊，再次證明此技術為反應動態學研究上強力的工具之一。

The reaction of N (2D) + C3H6 was investigated by crossed molecular beam technique and quantum-chemical calculations. Nitrogen atom was generated by a high-voltage discharge device. The collision energy is about 5.3 kcal mol-1. The products are ionized by a tunable VUV radiation then selected by a quadrupole mass filter. Finally we obtained the time-of-flight spectra of products. After simulating the time-of-flight spectra, we obtained the distribution of translational energy and the distribution of angular distribution under center of mass frame. In order to realize the dynamics of this reaction, we calculated the potential energy surface (PES) of this reaction by quantum-chemical calculations of density functional theory and coupled cluster. There are three product channels: C3H5N + H, C3H4N + 2H and C2H3N + CH3. Using the maximum translational energy of translational energy distribution and PES, we suggested that the structure of products are H2CHNCH2 + H, CH3CHCN + 2H and c-CH2(N)CH + CH3, respectively . The reaction pathway is mainly through the addition of N(2D) to πbond on the C3H6, then form a cyclic intermediate. The cyclic intermediate forms the products directly or after isomerization then forms the products. Compared with the past result of reaction N (2D) + C2H4, only one product channel C2H3N + H is observed. The angular distribution of C2H3N is partial to forward. But compared with the similar product channel C3H5N+H of reaction N (2D) + C3H6, the angular distribution of C3H5N is partial to backward. The different shows that the pathways of these two reactions to generate a hydrogen atom are not the same. The angular distribution of CH3CHCN is isotropic. It implies that the formation of CH3CHCN is through multiple isomerizations. The experimental results of reaction N (2D) + C2H4 didn’t report the formation of C2H2N + 2H. The angular distribution of c-CH2(N)CH is partial to forward. It implies that the formation of c-CH2(N)CH is through a short-lived complex. Using crossed molecular beam technique and PES of quantum-chemical calculations, we demonstrated the informations of reaction N (2D) + C3H6. And the results testify again that this technique is a powerful tool for research of chemical reaction dynamics.