鄰氯苯甲醚與間氯苯甲醚的第一電子激發態暨游離態振動光譜研究

Vibronic and Cation Spectroscopy of o-chloroanisole and m-chloroanisole

黃信彰(Hsin-Chang Huang)

指導教授 ： 金必耀 ； 曾文碧

國立臺灣大學/理學院/化學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.03378

摘要

我們利用單色共振雙光子游離(1C-R2PI)、光游離效率曲線(PIE curve)以及質量解析臨界游離(MATI)光譜法，探討鄰氯與間氯苯甲醚(o-, and m-chloroanisole)的分子特性，得到新的訊息包括分子於基態躍遷至第一電子激發態的精確躍遷能量、絕熱游離能、以及分子於第一電子激發態暨離子態的振動光譜。
　　鄰氯苯甲醚於光譜紀錄到唯一構型，配合理論計算顯示分子於第一電子激發態暨離子態呈反式結構，並得到分子的第一電子躍遷能和絕熱游離能分別為35745 ± 2, 66982 ± 5 cm-1；間氯苯甲醚於光譜紀錄到兩種構型，配合理論計算顯示分子於第一電子激發態暨離子態有順、反兩種穩定結構，記錄到對應的第一電子躍遷能和絕熱游離能分別為35822 ± 2, 35868 ± 2 cm-1以及67645 ± 5, 68008 ± 5 cm-1。
　　此外，我們也透過ab initio及密度泛函數理論等計算方法，與實驗結果及相關文獻進行比對，結果顯示大部分譜峰對應到苯環平面、以及取代基為主的振動運動。於目前儀器的解析極限，鄰氯與間氯苯甲醚同位素異構物有相同躍遷能量、絕熱游離能，且彼此振動頻率相近，顯示氯的同位素效應於此類分子系統影響並不顯著。透過實驗與光譜分析工作，使我們更加瞭解同位素效應，以及取代基對分子結構、躍遷能量、與振動運動之影響。

關鍵字

鄰氯苯甲醚 ； 間氯苯甲醚 ； 第一電子激發態 ； 離子態 ； 振動光譜

並列摘要

Here We present the resonance enhanced multiphoton ionization (REMPI) , the photoionization efficiency (PIE) curve, and the mass-analyzed threshold ionization (MATI) spectra of o-, and m-chloroanisole. o-chloroanisole is found to have only one stable structure whose excitation and adiabatic ionization energy are 35745 ± 2 and 66982 ± 5 cm-1, respectively. The vibronic features of m-chloroanisole are built on 35822 ± 2 and 35868 ± 2 cm-1 corresponding to the band origins of S1 ← S0 electronic transition (E1’s) for cis and trans rotamers. The adiabatic ionization energies (IEs) for these two species are found to be 67645 ± 5 and 68008 ± 5 cm-1, respectively.
　　The excitation and ionization energies between 35Cl and 37Cl isotopomers for these two molecules are found to be the same within present detection limit. Moreover, spectral features between isotopomers are almost the same, and their vibrational frequencies only differ by a few wavenumbers, which may results from the little change in system reduced mass and lower degree of Cl atom involed in the acive molecular motions. According to our experimental findings, the isotope effect caused by Cl substituent is negligible for o-, and m-chloroanisole.
　　Most of the active vibrations of o-, and m-chloroanisole in electronically excited S1 and cationic ground D0 states is assigned as the substituent-active and in-plane ring vibrations. By comparing these data with those of p-chloroanisole and other similar molecular systems, we can learn more about the vicinal substitution effects not only on electronic transition, ionization, but also molecular vibrations resulting from the relative locations of the Cl and OCH3 substituents.

並列關鍵字

o-chloroanisole ； m-chloroanisole ； vibronic spectroscopy ； cation spectroscopy ； mass analyzed threshold ionization spectroscopy

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