4-氯苯乙烯之第一電子激發態暨離子態振動光譜研究

Abstract

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記錄4-氯苯乙烯的第一電子激發態暨離子態光譜，精準地量測電子躍遷能(E1)和游離能(IE)，以及這個分子的活化振動，用以討論分子特性。 由實驗測得4-氯苯乙烯的E1和絕熱IE分別為33977  2及67972  5 cm-1，由於目前的儀器解析度極限，35Cl與37Cl的4-氯苯乙烯同位素異構物具有相同的E1和絕熱IE。由於兩倍的第一電子躍遷能(E1)稍小絕熱IE，我們必須利用雙色共振雙光子游離技術才能測得正確的E1和第一電子激發態光譜。 比較4-氯苯乙烯與氯苯、苯乙烯及苯的實驗的數據，我們發現在絕熱游離能存在添加規則(additivity rule)，也意味著4-氯苯乙烯分子內的乙烯和氯取代基之間的作用力是微弱的。此外，我們也利用從頭計算法(ab inito)及密度泛函理論計算與實驗結果對照，以利合理的解釋我們取得的實驗數據。

關鍵詞 : 4-氯苯乙烯, 質量解析臨界游離光譜術, 離子態光譜We applied the resonant two-photon ionization and mass-analyzed threshold ionization techniques to record the vibronic and cation spectra of 4-chlorostyrene to get the precise S1 ← S0 excitation energy (E1), adiabatic ionization energy (IE) and vibrational frequency to investigate ther molecular properties. The band origins of E1 of 35Cl-4-Chlorostyrene and 37Cl-4-chlorostyrene both appear at 33977 ± 2 cm-1. The mass-analyzed threshold ionization (MATI) spectra give the IE of 67972 ± 5 cm-1 for both isotopologues. Because the E1 is smaller than one half of the IE, we used the two-color resonant two-photon ionization (2C-R2PI) technique to measured the E1 and the vibronic spectrum. Comparing the E1‘s and IEs of 4-chlorostyrene, chlorobenzene, and styrene we have found an additivity rule which implies weak interactions among the Cl and vinyl substituents. We have also performed the ab initio and density functional theory calculations which help us in spectral assignment and support our experimental findings.

Keyword : 4-chlorostyrene, mass-analyzed threshold ionization spectroscopy, ionization spectroscopy