本篇論文使用飛秒激發-探測及光游離-光分解技術，觀察MPEA (N-methylphenylethylamine)及MNMA (N-methyl-1,2,3,4-tetrahydronaphthalen-2-amine)陽離子的緩解動態學過程。首先使用波長266 nm的飛秒激發脈衝透過分子苯環端的S1 state，以1+1共振增強多光子游離技術將苯環端局部游離並激發至其D1/D2 state，隨後再使用另一道波長範圍600~1500 nm的飛秒探測脈衝偵測陽離子由D1/D2 state緩解至D0 state的動態學過程，並以理論計算的結果協助解釋。MPEA陽離子由D1/D2 state緩解至D0 state的電荷轉移常數(τCT)為2.9 ps，陽離子在D0 state構型緩解再平衡過程的時間常數約為87 ps。MPEA陽離子超快時間解析光分解光譜的尖峰位於1100 nm附近，為陽離子在D0 state的吸收。而MNMA陽離子由D1/D2 state緩解至D0 state的τCT為18 ps，陽離子在D0 state構型緩解再平衡過程的時間常數約為374 ps。MNMA陽離子超快時間解析光分解光譜中位於1200 nm及750 nm出現兩吸收譜帶，分別為陽離子在D1/D2 state及D0 state的吸收，隨著延遲時間增加，兩吸收譜帶呈現消長的趨勢，反映電荷轉移過程的發生。MNMA分子結構上受到剛性環的限制，加上其碳橋上的碳數較MPEA分子多，使得其電子供給端與電子受體端在空間中的距離可能較遠，故MNMA陽離子的τCT較MPEA陽離子的τCT長。

We employed femtosecond pump-probe photoionization-photofragmentation (fs-PIPF) spectroscopy to study ultrafast charge transfer (CT) dynamics in N-methylphenylethylamine (MPEA) and N-methyl-1,2,3,4-tetrahydronaphthalen-2-amine (MNMA) cations. We used 1+1 REMPI to selectively ionize their phenyl group via their S1 state to reach the cation D1/D2 state, in which the positive charge is more localized in the phenyl ring. The subsequent relaxation dynamics occurring in the cations is then probed by delayed femtosecond laser pulses that result in ion fragmentation. Ion depletion transients were measured by monitoring the ion signal as a function of pump-probe delay time, and the probe laser wavelength was varied between 600-1500 nm to obtain ultrafast time-resolved ion photofragment spectra. For MPEA, the charge transfer time constant (τCT), which corresponds to the internal conversion from the D1/D2 state to D0 state, is about 2.9 ps. The time constant τ3, which was assigned to the equilibrium among conformers in the D0 state, is about 87 ps. The ultrafast time-resolved ion photofragmentation spectrum of MPEA cation exhibits a maximum at 1100 nm and was assigned to the absorption of D0 state cations. For MNMA, the τCT is about 18 ps, and the τ3 is about 374 ps. There are two bands in MNMA cation ultrafast time-resolved ion photofragmentation spectrum, of which the 1200 nm band is due to the absorption of cation D1/D2 state, and the 750 nm band is due to the absorption of D0 state. We observed that the absorption of the D1/D2 state cations decreases slowly with increasing delay time, while the absorption of D0 state cations gradually rises. The complementary temporal behavior of these two species provides a strong evidence for the charge transfer process. Due to the rigidity in MNMA and the fact that the number of carbon atoms in the carbon bridge in MNMA is more than that in MPEA, the distance between electron donor and acceptor is longer in MNMA cation, so the τCT of MNMA cation is longer than that of MPEA cation.

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