https://scholars.lib.ntu.edu.tw/handle/123456789/178483
標題: | 合環芳香性分子質量解析臨界光譜 MATI Spectroscopy of Fused Ring Aromatic Molecules |
作者: | 李奕璋 Li, Yi-Chang |
關鍵字: | 光譜;質譜;Spectroscopy;MATI | 公開日期: | 2007 | 摘要: | Part I 我們應用高解析度共振雙光子游離與質量解析臨界游離光譜術來探討benzimidazole與benzotriazole分子在離子態特性,實驗所得到的數據包括精確的第一電子躍遷能和游離能,以及這些分子的S1電子激發態和D0離子基態的振動光譜。所測得benzimidazole的第一電子躍遷能和游離能分別為36022cm-1和67552cm-1,而benzotriazole的值分別為34917cm-1和70474cm-1。我們也進行量子化學及密度泛函數理論計算作為實驗的佐證,分析實驗的結果顯示benzimidazole在S1和D0態時表現出來大部份為芳香環平面上的運動,然而benzotriazole卻大部份為非平面N2–H 和 N1N2N3的擺動。所測得的游離能分別較indole大4961 cm-1及7883 cm-1。表示因為氮原子具有較大拉電子的能力,因此五角環上具有較多的氮原子會使得分子具有較高的游離能。 Part II 我們使用單色共振雙光子游離光譜術與高解析度質量解析臨界游離光譜術來研究2,4,7-methylindole在第一電子激發態及離子態的分子特性。精準地量測第一電子躍遷能和游離能,並記錄這些分子的 S1電子激發態和D0離子基態的振動光譜。所測得的2,4,7-methylindole電子躍遷能分別為35161cm-1、35105 cm-1及35176cm-1,所量測之游離能分別為60482 cm-1和61222 cm-1及61490 cm-1。所觀測到的分子振動包括低頻的甲基轉動、平面和非平面的indole環振動,相關譜線的強弱卻隨不同的結構異構物而有異。例如:甲基低頻的轉動主要出現在2、7-methylindole光譜中,然而4-methylindole的光譜卻幾乎沒有分子內甲基轉動振動的訊號,這些觀察指出取代基的特性與取代基在苯環上的位置都會影響分子的振動以及電子躍遷能。比較我們所得到的實驗數據和indole、1-methylindole 中證明了這些分子在游離時主要是發生在五角環上。我們所作理論計算的結果亦支持實驗所得的數據。 Part I We applied high-resolution resonant two photon ionization and mass analyzed threshold ionization spectroscopy to investigate the cationic properties of benzimidazole and benzotriazole. The obtained experimental data include the first electronic transition energy (E1) and ionization energy (IE) as well as the active vibrations in the electronically excited S1 and cationic ground D0 states. The E1 and IE of benzimidazole are determined to be 36022 cm-1 and 67552 cm-1, whereas those of benzotriazole are 34917 cm-1 and 70474 cm-1, respectively. We also performed ab initio and density functional calculations to support our experimental findings. Analysis of our experimental results shows that most of the active modes of benzimidazole in the S1 and D0 states are related to in-plane vibrations of the aromatic bicyclic ring, whereas those of benzotriazole correspond to the out-of-plane N2–H and skeleton N1N2N3 bending vibrations. It is found that the IEs of benzimidazole benzotriazole are greater than that of indole by 4961 cm-1 and 7883 cm-1, respectively. This indicates that the IE of these aza-aromatic bicyclic molecules increases with the number of the N atoms. This finding may be attributed to the nature and the N atoms in the five-membered ring. Part II We applied high-resolution resonant two photon ionization and mass analyzed threshold ionization spectroscopy to study the molecular properties of 2, 4 and 7-methylindole (2, 4 and 7MI) in the electronically excited S1 and cationic ground D0 states. Analysis of the obtained spectra give information about the precise first electronic transition energy (E1) and ionization energy (IE) as well as the active vibrations in the S1 and D0 states. The E1’s of 2, 4 and 7MI are determined to be 35161cm-1、35105cm-1 and 35176cm-1, whereas the IEs are determined to be 60482, 61222 and 61490cm-1, respectively. The observed active vibrations include CH3 torsion and the in-plane and out-of-plane vibrations of the indole ring. It is found that the low-frequency CH3 torsion are active for the 2MI and 7MI cations but inactive for the 4MI cation. This indicates that the nature and the location of the substituent can influence the molecular vibrations in addition to the transition energies. Comparing these data with those of indole and 1-methylindole suggests that the methyl substitution on the pyrrole part leads to a grater redshift in the IE than on the benzene part. These experimental findings are well supported by our theoretical calculations. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/51988 | 其他識別: | zh-TW |
顯示於: | 化學系 |
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ntu-96-R94223071-1.pdf | 23.31 kB | Adobe PDF | 檢視/開啟 |
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