N,N-二甲基-3-苯基丙基胺陽離子內之超快光游離誘發電荷轉移動態學研究

Ultrafast Photoionization-Induced Charge Transfer Dynamics in N,N-dimethyl-3-phenylpropylamine Cation

曾繁彊(Fan-Chiang Tseng)

指導教授 ： 鄭博元

國立清華大學/理學院/化學系所/碩士(2019年)

摘要

我們利用飛秒激發-探測光游離-光裂解(Femtosecond Pump-Probe Photoionization-Photofragmentation)光譜術結合質譜偵測技術研究N,N-dimethyl-3-phenpropylamine (DMPPA), N-methylphenyl-3-propylamine (MPPA) 及3-phenylpropylamine (PPA)陽離子的電荷轉移反應及離子基態構型緩解動力學，並比較與實驗室前人對2-phenylethyl-N,N-dimethylamine (PENNA)、N-methyl-2-phenylethylamine (MPEA)與2-phenylethylamine (PPA)之實驗結果有何異同。我們利用1+1 共振多光子游離(Resonance Multiphoton Ionization, REMPI)技術使處於基態(S0)之分子吸收兩個波長為266.1 nm的激發雷射光子，先到達S1 state後再被游離，接著導入波長為798.3 nm的探測雷射將其激發至更高的離子激發態後碎裂。透過調整探測脈衝與激發脈衝間的延遲時間並擷取離子訊號，我們可以得到離子瞬時光譜。我們使用連續反應動力學模型適解所得到的離子瞬時光譜。DMPPA+ 與PPA+的損耗瞬時光譜皆得到三個時間常數，而MPPA+的瞬時光譜則得到兩個。我們同時也量測苯丙醇(3-phenyl-1-propanol, PPAL+)的離子損耗瞬時光譜並進行適解，由於PPAL+不會進行電子轉移，故將PPAL+適解出的時間常數與DMPPA+、MPPA+和PPA+之時間常數比較，即可判斷屬於電子轉移的時間常數。由於次皮秒等級的時間常數在PPAL+之瞬時光譜未被觀察到，而只出現在DMPPA+、MPPA+和PPA+之瞬時光譜，故我們認為此次皮秒時間常數屬於電子轉移，DMPPA+、MPPA+及PPA+這些陽離子內的電子轉移過程分別約為0.18、0.24及0.17 ps，而之後數皮秒至十幾皮秒的過程在PPAL+的瞬時光譜中亦有出現，因此可歸為自陽離子之弗蘭克-康登(Franck-Condon)構型緩解至陽離子基態(D0)穩定結構之過程。

關鍵字

電子轉移 ； 飛秒雷射 ； 飛行時間質譜儀 ； 氣相

並列摘要

We studied the ultrafast charge transfer and conformational relaxation dynamics of N,N-dimethyl-3-phenpropylamine (DMPPA), N-methylphenyl-3-propylamine (MPPA) and 3-phenylpropylamine (PPA) cations by utilizing femtosecond pump-probe photoionization-photofragmentation spectrometry along with time-of-flight mass spectrometry. We also compared the results with those of 2-phenylethyl-N,N-dimethylamine (PENNA), N-methyl-2-phenylethylamine (MPEA) and 2-phenylethylamine (PPA). Neutral DMPPA, MPPA and PPA seeded in a helium free jet are photoionized by femtosecond 1+1 resonance-enhanced multiphoton ionization via their S1 state, and the subsequent dynamics occurring in the cations is probed by delayed pulses that result in ion fragmentation. With a sequential first-order kinetic model, three time constants are obtained from the depletion transients of DMPPA+ and PPA+, respectively, while for MPPA+ we only found two time constants. Comparing the results with that of 3-phenyl-1-propanol (PPAL+), which does not undergo charge transfer, we assigned the sub-picosecond time constants of DMPPA+ (0.18 ps), MPPA+ (0.24 ps) and PPA+ (0.17 ps) to the charge transfer dynamics, and the rest are assigned to conformational relaxation dynamics, where the cations go from their Franck-Condon structures to the cation ground state(D0) stable conformation after charge transfer.

並列關鍵字

charge transfer ； femtosecond laser ； time-of-flight mass spectrometer ； gas phase

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