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利用飞秒时间分辨的光电子影像技术研究了2-甲基呋喃分子激发态超快非绝热动力学。2-甲基呋喃分子吸收两个400 nm的光子后同时被激发到n=3的里德堡态S1[~1A′′(π3s)]、~1A′(π3p_x)、~1A″(π3p_y)、~1A″(π3p_z)和价电子态~1A′(ππ*),之后被两个800 nm的光子电离。通过母体离子产率随泵浦-探测延迟时间的变化曲线测得这些里德堡态与价电子态的平均寿命为50 fs。通过解析光电子能谱中n=3的里德堡态与价电子态所对应的组分峰的相对演化特征,观测到了这些激发态之间的内转换过程,并且揭示了价电子态~1A′(ππ*)在内转换过程中扮演的重要“纽带”作用。里德堡态与价电子态之间的混合,形成势能面间的锥形交叉,导致了如此超快的内转换过程。
The fast and non-adiabatic kinetics of 2-methylfuran excited states were studied using femtosecond time-resolved photoelectron imaging. 2-Methylfuran molecules absorb both 400 nm photons and are simultaneously excited into the Rydberg states S1 [~ 1A ’(π3s)], ~ 1A’ (π3p_x), ~ 1A “(π3p_y) at n = , ~ 1A ”(π3p_z) and valence state ~ 1A ’(ππ *), followed by two 800 nm photons. The average lifetimes of these Rydberg states and valence states as measured by the parent ion yield versus pump-probe delay time are 50 fs. By analyzing the relative evolution characteristics of the component peaks corresponding to the Rydberg states and the valence states of n = 3 in photoelectron spectroscopy, the internal transitions between these excited states were observed and the valence states ~ 1A ’ (ππ *) plays an important role in the process of conversion. The mixing between the Rydberg states and the valence states leads to the conical intersection between the potential surfaces, resulting in such an ultra-fast internal conversion process.