2-氯-4-氟苯甲醚之質量解析臨界游離光譜研究

Abstract

本實驗應用單色共振雙光子游離(1C-R2PI)光譜術、雙色共振雙光子游離(2C-R2PI)光譜術以及質量解析臨界游離(MATI)光譜術來探討2-氯-4-氟苯甲醚的分子特性，利用以上技術精準量測分子於基態躍遷至第一電子激發態的能量、絕熱游離能及其第一電子激發態暨離子態的振動光譜。 利用單色共振雙光子游離術與質量解析臨界游離光譜術，測得2-氯-4-氟苯甲醚和其同位素異構物(37Cl)有相同的第一電子躍遷能和絕熱游離能，分別為34621 ± 2 cm-1及67204 ± 5 cm-1，藉由第一電子激發態振動光譜的資訊，以不同中間態S100、S1X1、S1151、S16b1紀錄離子態振動光譜，依據實驗結果搭配理論計算，顯示大部分振動模式和苯環平面運動及取代基運動有關。 將2-氯-4-氟苯甲醚與實驗室之前所測量過的2-氯苯甲醚、4-氟苯甲醚、苯甲醚以及2,4-雙氟苯甲醚的實驗數據做比較，讓我們更加了解氯和氟在苯甲醚上的取代基效應，以及對分子結構、躍遷能量的影響。利用理論計算的結果來解釋我們所觀察到的現象，並幫助我們完成分子光譜的標定。In this work we applied the resonant two-photon ionization and mass-analyzed threshold ionization techniques to investigate the molecular properties of 2-chloro-4-fluoroanisole. These techniques are used to record the vibronic and cation spectra which also determine the excitation energy and adiabatic ionization energy. The excitation energy of the S1←S0 transition (E1) and the adiabatic ionization energy (IE) of 2-chloro-4-fluoroanisole are found to be 34621 ± 2 cm-1 and 67204 ± 5 cm-1, respectively. Between 35Cl and 37Cl isotopomers for 2-chloro-4-fluoroanisole has the same excitation and ionization energies within present detection limit in our experiment. The cation spectra were obtained by ionizing via the 00, X1, 151, and 6b1 levels of the electronically excited S1 state. According to experimental results with theoretical calculations, the most of active vibrations of this molecule in S1 and D0 states are related to in-plane aromatic ring and substituent-active vibrations. Comparing the data of 2-chloro-4-fluoroanisole with those of o-chloroanisole, p-fluoroanisole, anisole, and 2,4-difluoroanisole, we can learn more about the substitution effects on the transition energy and molecular geometry. By using theoretical calculation results can explain phenomena that we observe in the experiment, and help us to assign the peaks from molecular spectra.