在本篇論文中，我們利用飛秒激發-探測技術搭配光游離光裂解機制測量MNA (N-methyl-1,2,3,4-tetrahydronaphthalen-2-amine)及MPBA (methyl(4-phenylbutyl)amine)陽離子激發態的緩解動態學行為。我們以266 nm的飛秒脈衝雷射透過1+1 共振多光子游離技術，經過苯環端局部S1 state使分子吸收兩顆激發光子將苯環端局部游離，使它到達離子態D1 state。我們在不同的激發-探測延遲時間導入探測脈衝，使緩解中的陽離子吸收探測光子能量進而裂解，記錄離子損耗訊號隨激發-探測延遲時間之變化即可獲得離子損耗瞬時訊號。我們使用連續動力學模型對所測得的MNA與 MPBA離子損耗瞬時訊號進行擬合，結果發現皆可獲得三個時間常數τ1，τ2和τ3。我們將τ1指認為陽離子D1 態快速的分子內振動能重新分配行為，τ2代表陽離子由D1 state經由內轉換緩解至D0 state，此過程相當於苯基端上的正電荷移轉至胺基端，或是胺基上的電子移轉到苯基端上，故為一電荷轉移過程，τ3則為陽離子在緩解至D0 state時在不同構型間再平衡過程。我們測到的MNA與MPBA的τ2分別為9.3與6.6 ps，為了支持我們對τ2之指認，我們以相同技術研究無電荷轉移反應的PPN (3-phenylpropionitrile)陽離子，結果並沒有觀察到上述類似時間量級的緩解過程，這強力支持了τ2為電荷轉移時間常數之指認。綜合本論文與本實驗室前人之研究結果，我們發現這一系列離子內電荷轉移速率常數與平均RN-Ph的變化概略符合指數衰減趨勢，亦即當平均RN-Ph距離越長則電荷轉移越慢，這顯示影響電荷轉移速率的因素之一為空間直線距離而非碳鏈的長度。

In this study, we used femtosecond pump-probe photoionization-photofragmentation spectroscopy to study ultrafast charge transfer (CT) dynamics in N-methyl-1,2,3,4-tetrahydronaphthalen-2-amine (MNA), and methyl(4-phenylbutyl)amine (MPBA) cations. We used 1+1 resonance-enhanced multiphoton ionization to locally ionize their phenyl group via their S1 state by absorbing two pump photons and probed the subsequent relaxation dynamics in the cations by using a delayed femtosecond probe pulse that results in ion fragmentation. We acquired ion depletion transients by monitoring the parent ion signals as a function of pump-probe delay time. Using a consecutive kinetics model to fit the ion depletion transients, we obtained three time constants (τi). We assigned τ1 to the rapid intramolecular vibrational energy redistribution (IVR) of the initially ionized cationic D1 state. The time constant 2 was assigned to the internal conversion from the cation D1 to D0 ground state, corresponding to the shift of the positive charge initially localized in the phenyl ring to the amino group, and therefore it corresponds to a CT process. The time constant 3 was assigned to the conformational relaxation in the D0 state to establish the final equilibrium distribution. In this work CT time constants for MNA and MPBA cations were found to be about 9.3 and 6.6 ps. In order to support our assignment for τ2, we used the same method to study PPN (3-phenylpropionitrile), a cation in which CT is not possible energetically, and we did not observe any relaxation dynamics in similar time scales to those mentioned above. This strongly supports the assignment of τ2 to charge transfer. Combining results of this thesis and those reported by former group members of our laboratory, we found that the dependence of the CT rate on the average distance between the nitrogen atom and the phenyl ring (RN-Ph) in this series of cations roughly conforms with an exponential decay relation, that is, the longer the average RN-Ph distance is, the slower the charge transfer becomes. This shows that one of the factors affecting the rate of charge transfer is the straight-line distance in space rather than the length of the separating carbon chain.

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