利用超快光游離誘發氣相2-苯基乙基-N,N-二甲基胺陽離子內之電子轉移動態學研究

Ultrafast Photoionization Induced Electron-Transfer Dynamics in 2-phenylethyl-N,N-dimethylamine Cation in Gas Phase

呂柏昱(Po-Yu Lu)

指導教授 ： 鄭博元

國立清華大學/理學院/化學系所/碩士(2018年)

摘要

在本論文中，我們利用飛秒雷射激發-探測光游離-光裂解技術(femtosecond pump-probe photoionization-photofragmentation spectroscopy)結合質譜偵測技術，研究2-苯基乙基-N,N-二甲基胺(PENNA)陽離子的電子轉移及相關動力學，並試圖與Schlag團隊的實驗結果做比較和探討。我們以1+1 REMPI技術(λpump = 265.9 nm)游離化PENNA，再藉由導入探測雷射(λprobe = 797.7 nm)得到PENNA離子碎裂強度隨時間變化的瞬時訊號。我們利用三組時間常數適解該瞬時訊號，分別是τ1≈ 0.15 ps、τ2≈ 18 ps與τ3≈ 56 ps。為了要進一步地指認何者為電子轉移，我們亦觀測苯乙醇(PEAL)、2-苯基乙基-N-甲基胺(MPEA)與2-苯乙胺(PEA)的離子瞬時訊號，其中PEAL在本實驗條件下並不會發生電子轉移，而MPEA與PEA分別為PENNA去掉一個和兩個甲基。利用PEAL陽離子損耗瞬時光譜適解出來的結果與其他三者比對，可以幫助我們排除不是電子轉移的時間常數，而MPEA與PEA的陽離子損耗瞬時光譜的適解，則可以讓我們觀察這個系統(包含PENNA)是否會有一系列具關聯性的變化。適解並比較分析的結果顯示出PENNA、MPEA與PEA陽離子都有一個次皮秒等級的τ_1，而此一成分在PEAL陽離子並未被觀察到，故我們將其指認為電子轉移。而PEAL陽離子我們只用兩組時間常數便可以很好地適解，其動態行為我們認為與PENNA+、MPEA+與PEA+上也會觀察到的τ2及τ3類似，是從陽離子FC態緩解到最穩定結構的過程。

關鍵字

電子轉移 ； 氣相 ； 超快化學

並列摘要

We studied the ultrafast electron transfer (ET) dynamics in the cations of 2-phenylethyl-N,N-dimethylamine (PENNA) after photoionization using the femtosecond pump-probe photoionization-photofragmentation (fs-PIPF) spectroscopy compared our experimental results with these reported by the Schlag's group. We photoionized PENNA in a supersonic beam with fs pump pulses at 265.9 nm with 1+1 REMPI via its S1 origin using the phenyl group as the chromophor, producing PENNA cation predominately in its first excited state (D1). The resulting PENNA cations were then probed by a second fs pulse at ~800 nm by exciting the evolving ionic system to higher excited states, which enhance the fragmentation yield of the cation. We used a consecutive reaction kinetics model including three time steps to fit the parent ion depletion transient signals, and the results are τ_1≈ 0.15 ps, τ_2≈ 18 ps and τ_3≈ 56 ps. To identify which one corresponds to the ET reation, we also carried out similar experiments for 2-phenylethylalcohol (PEAL), 2-phenylethyl-N-methylamine (MPEA) and 2-phenylethylamine (PEA). The results show that PENNA+, MPEA+ and PEA+ transients all contain a sub-ps component that is not observed in PEAL+ transient. For this reason, we attributed the sub-ps time constant to the the ET reaction. The two time constants we used to fit the PEAL+ transient are like the τ_2 and τ_3 in PENNA+, MPEA+ and PEA+, and are assigned to the conformational relaxations from the cation FC state to the most stable conformation.

並列關鍵字

electron transfer ； gas phase ； ultrafast

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