- 學位論文
芳香及有機金屬分子的質量解析臨界游離光譜研究
Aromatic molecules and sandwich organometallics studied by mass-analyzed threshold ionization spectroscopy
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摘要
利用單色共振雙光子游離、雙色共振雙光子游離(R2PI)與質量解析臨界游離光譜術(MATI)來探討結構異構物臨氟苯乙烯(2-fluorostyrene)和間氟苯乙烯(3-fluorostyrene)；4-氯-2-氟苯甲醚(4-chloro-2-fluoroanisole) ；3-氯-5-氟苯胺(3-chloro-5-fluoroaniline)；三明治有機金屬分子bis(η6-biphenyl)chromium ((η6-Ph2)2Cr) ；(η6-biphenyl)(η6-methylphenyl)chromium ((η6-Ph2)(η6-PhMe)Cr) ；(η7-cycloheptatrienyl)(η5-cyclopentadienyl)chromium ((η7-C7H7)(η5-C5H5)Cr) 的特性。本實驗精確量測到相當多新的訊息，包括從基態到第一電子激發態的躍遷能(excitation energy)、絕熱游離能(adiabatic ionization energy)及其在第一電子激發態和離子態的振動光譜，並使用ab initio及密度泛函理論來做理論計算預測分子結構、振動、躍遷能及游離能來強化本實驗的結果，除此之外，亦針對上述實驗結果和類似的分子做分析比較。 由於立體障礙的影響，實驗結果及理論計算皆顯示2-fluorostyrene和4-chloro-2-fluoroanisole僅存在trans的旋轉異構物。然而，在3-fluorostyrene的實驗中，由於兩官能基空間距離較遠的關係，同時觀察到此分子兩種不同的旋轉異構物，理論計算也可以得到和實驗數據相呼應的結果。 文中更整理了本實驗室過去的芳香分子相關研究，得到臨、間、對(ortho-, meta-, para-)三種結構異構物在大部分情況下，其絕熱游離能呈現meta-＞ortho-＞para-的相對關係，我們簡稱MOP rule；另外，由本實驗室過去研究統整發現，很多分子其取代基造成的躍遷能變化具有可以加乘的特性(additivity rule)，本實驗中氟和氯取代基正是符合其加成特性的例子，此法可以快速的預測躍遷能所在範圍，有利於加速實驗進行，對於光譜學的研究有很大的幫助。 另外，本論文更探討了未被探討過的1,3,5-三取代芳香烴類分子的特殊振動光譜類型，不同於以往以平面環運動為主的光譜，而是以低頻非平面振動為主，這方面資訊從未有文章探討過，本文將會對這類型光譜進行分析和譜峰標定的工作。 除了芳香烴類分子的研究之外，本實驗室更致力於三明治有機金屬分子光譜的研究，此類分子合成困難、結構易被破壞再加上需在無氧或低氧環境下操作，使得這類分子的光譜非常難以取得。本實驗使用由研究助理曾聖淵近期設計的新式進樣方法，克服三明治分子低蒸氣壓所造成的噴頭阻塞問題，成功得到(η6-Ph2)2Cr、(η6-Ph2)(η6-PhMe)Cr和(η7-C7H7)(η5-C5H5)Cr三種有機金屬三明治分子的光譜資訊，這些全新的資訊對於此類合成困難的三明治分子有很好的定性分析的作用，也能提供更多的分子振動資訊。
並列摘要
Two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopy was applied to study the vibrationally resolved cation spectra of structural isomers of 2-fluorostyrene and 3-fluorostyrene; 4-chloro-2-fluoroanisole; 3-chloro-5-fluoroaniline;sandwich organometallics incusing bis(η6-biphenyl)chromium ((η6-Ph2)2Cr), (η6-biphenyl)(η6-methylphenyl)chromium ((η6-Ph2)(η6-PhMe)Cr) and (η7-cycloheptatrienyl)(η5-cyclopentadienyl)chromium ((η7-C7H7)(η5-C5H5)Cr). The S1←S0 electronic transition and the adiabatic ionization energies of these molecular species have been precisely measured. Along with this, we performed ab initio and density functional theory calculations to predict the molecular structure, vibration, and electronic transition and ionization energies to support our experimental findings. Moreover, we compare these experimental findings with respective similar molecular species to gain knowledge about molecular properties. Because of stereo effect, both experimental data and theoretical calculation results show that only the trans form of 2-fluorostyrene and 4-chloro-2fluorostyrene involve in the excitation and ionization processes. On the contrary, two stable species of 3-fluorostyrene were observed in the experiment. They were confirmed to be the cis and trans rotational isomers (rotamers) by our quantum chemical calculations. By comparing all the experiments of aromatic molecules performed by our group in the past, one can find that the adiabatic energies of structural isomers follow the order: meta-＞ ortho-＞ para-, which we called “MOP rule.” Besides, our experimental data shows that there may exist an “additivity rule” associated with the energy shift resulting from the additional fluorine or chlorine substituents. By using these rules, we can reasonably predict the electronic transitional energy and ionization energy, which and speed up our laser spectroscopic experiments. In addition, we have also recorded the spectra of some sandwich organometallics. These spectroscopic data are very rare in the literature. Possible reasons are as follows. The sandwich organometallic compounds are hard to be synthesized. Because they can decompose quickly in the atmosphere, the experiments should be performed in an oxygen-free environment. To gain enough vapors and to avoid clogging in the molecular beam valve, we designed a special pulsed molecular valve. With this valve, we succeeded in recording the vibronic, PIE, and MATI spectra of (η6-Ph2)2Cr and (η6-Ph2)(η6-PhMe)Cr. These new spectra are very helpful for us to learn photophysics of these sandwich organometallic molecules.
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