本論文研究protic solvent—水、甲醇與aprotic solvent—四氫呋喃與胞嘧啶形成之為溶合團簇之激發態衰減動態學。我們利用飛秒雷射激發–探測多光子游離技術結合飛行時間質譜儀進行實驗，以激發波長為266 nm；探測波長為800 nm之pump-probe REMPI(1+3')游離氣相胞嘧啶與溶劑分子所形成的團簇，觀察離子訊號大小隨激發–探測脈衝時間差變化。胞嘧啶在氣相中有三種較穩定的互變異構物—keto、enol、imino結構，在胞嘧啶單體的氣相動力學實驗中可以看見兩種生命期，分別為keto與enol構型的貢獻。但當胞嘧啶(Cy)在分子束在與protic solvent分子影響下，瞬時光譜中只會看見keto結構的貢獻。與前人的實驗相比，發現Cy-(H2O)n=2-6的生命期都約為0.2 ps，和在液態水相的胞嘧啶動力學實驗有相似的時間尺度。Cy-(MeOH)1與Cy-(H2O)1瞬時光譜形狀相似，生命期都約為0.5 ps；而Cy-(MeOH)2和Cy-(MeOH)3的激發態衰減生命期分別為0.48 ps和0.33 ps 較Cy-(H2O)n>2長，推測可能是因為甲醇分子的極性與氫鍵都較水分子弱所造成。當胞嘧啶與aprotic solvent分子作用時，瞬時光譜形狀與胞嘧啶單體的瞬時光譜較相似。Cy-(THF)1的瞬時光譜包含兩個生命期，一個為keto構型的貢獻，生命期為0.48 ps，；另一為enol結構的貢獻，生命期為10 ps。由上述的生命期可知，四氫呋喃對enol結構的胞嘧啶影響較大，生命期長了兩倍以上。

Gas-phase ultrafast excited-state dynamics of cytosine(Cy)-(H2O)n=4-6, Cy-(MeOH)n=1-3, and Cy-(THF)1 micro-solvated clusters were investigated in molecular beams using femtosecond pump-probe photoionization spectroscopy at about 266 nm excitation to identify the effect of protic and aprotic solvents to the cytosine intrinsic dynamics. The results suggest that the presence of protic solvent molecules allows an extensive relaxation of Cy-(H2O)n=1-6, and Cy-(MeOH)n=1-3 to the lowest-energy tautomer isomers, but aprotic solvent molecules do not exhibit such behaviors. Excited-state lifetimes of Cy-(H2O)n=1-6 and Cy-(MeOH)n=1-3 measured here are 0.2-0.5 ps. On the other hand, there are two components in the Cy-(THF)1 transient: one with an excited-state lifetime of 0.48 ps, and the other ~ 10 ps. The shorter component is ascribed to the keto form of Cy-THF, whereas the longer component is attributed to the enol form of Cy-THF. Comparisons of the Cy-(THF)1 and cytosine monomer transients suggest that THF has a stronger effect on enol-cytosine than keto-cytosine.

摘要 I
Abstract II
第一章 序論 3
1.1 前言 3
1.2 文獻回顧 5
1.3 本論文研究目的 11
第二章 實驗系統與技術 12
2.1 激發-探測共振增強多光子游離技術 12
2.2 超快飛秒雷射系統 15
2.2.1 雷射產生源 15
2.2.2 能量再生放大器 21
2.3 波長調變器 28
2.3.1 倍頻與混頻技術 28
2.4 分子束系統 30
2.4.1 分子束樣品進氣裝置 34
2.5 飛行時間質譜儀 36
2.6 實驗架設圖 40
2.7 訊號擷取系統 41
2.8 測量實驗中IRF的FWHM 43
第三章 實驗數據與分析 45
3.1 胞嘧啶單體 45
3.1.1 雷射能量依存性 47
3.1.2 瞬時光譜與數據分析 52
3.2 胞嘧啶-溶劑分子團簇 54
3.2.1 Cy-(H2O)n=1,2,3 54
3.2.2 Cy-(H2O)n=4,5,6 55
3.2.3 Cy-(MeOH)n=1,2,3 62
3.2.4 Cy-(THF)1 66
3.3 實驗結果整理 69
3.4 理論計算數據分析 70
3.4.1 胞嘧啶的水合大團簇 71
3.4.2 胞嘧啶與甲醇結合之團簇 72
3.4.3 胞嘧啶與四氫呋喃結合之團簇 74
第四章 結果與討論 78
4.1 胞嘧啶的激發態衰減機制 78
4.2 胞嘧啶-甲醇團簇的激發態衰減 83
4.3 胞嘧啶-四氫呋喃團簇的激發態衰減 87
第五章 結論 90
參考文獻 92

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