酚-氨陽離子錯合物中之超快質子轉移反應動態學研究

Ultrafast Proton Transfer Reaction Dynamics in Phenol−Ammonia Cation Complex

陳依微(Yi-Wei Chen)

指導教授 ： 鄭博元

國立清華大學/理學院/化學系/碩士(2011年)

https://doi.org/10.6843/NTHU.2011.00135

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)結合質譜技術，研究在PhOH−NH3陽離子錯合物中的質子轉移反應以及相關動態學。我們觀察到PhOH−NH3陽離子錯合物之衰減過程可以由一起始尖峰和兩個時間常數來描述：t1＝0.8±0.2 ps、t2＝40±5 ps，此結果告訴我們當以錯合物苯酚的S1為中間態進行共振增益多光子游離時，可由苯酚的吸光團受激發躍遷到其離子能態，此時PhOH−NH3陽離子錯合物首先進行一個很快的vibrational dephasing或起始波包運動過程（<50 fs），此時質子開始在O及N間來回遊蕩，接著PhO繼續進行一個很快的分子內振動能量重新分配過程（~0.8 ps），而PhOH−NH3陽離子錯合物之起始結構回到最穩定結構約有0.3 eV的能量差，主要集中於O⋯H⋯N間，此熱反應中心能量分須分散到整個錯合物的其他振動模並隨著O⋯H⋯N間鍵間的變化進行質子轉移的過程而緩解能量，此過程須要約40 ps。此外我們亦比較錯合不同路易士鹼分子對錯合物陽離子態的動態行為所造成的影響，我們發現路易士鹼分子的質子親和力和錯合物回到最穩定的離子態結構時需緩解的能量皆會影響質子轉移的過程。

關鍵字

質子轉移 ； 錯合物 ； 陽離子動態學 ； 飛秒雷射

並列摘要

We report studies of ultrafast proton transfer reaction of PhOH−NH3 cation complex using femtosecond photoionization- photofragmentation spectroscopy.With 266 nm ionization, the observed transients for PhOH−NH3 cation complex are characterized by an ion depletion with an initial spike and two time constants of about 0.8 ps and 40 ps. The results support the mechanism in which PhOH−NH3 cation complex initially undergoes a fast vibrational dephasing or wave packet motion causing the proton wandering between O and N. Then, PhO undergoes a fast intramolecular vibrational energy redistribution (IVR) in about 0.8 ps. Due to a large structure change upon ionization, a large amount of vibrational energy mainly deposited in the reaction center:O⋯H⋯N. It takes about 40 ps to dissipate the energy along the pronton transfer coordinate to other vibrational modes and then the cation relaxes into the equilibrium structure. We also compare dynamics in complexes with different Lewis bases. The results also support the mechanism defined in PhOH−NH3 cation complex and suggest the proton affinity of bases being an important factor for the proton-transfer affect dynamics in complex.

並列關鍵字

proton transfer ； complex ； cation dynamics ； femtosecond laser

參考文獻

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