Ultrafast Dynamics of Benzene on the S-2 State Investigated by Femtosecond Time-Resolved Photoelectron Spectroscopy

The ultrafast dynamics of benzene on the S2 state have been investigated by femtosecond.time-resolved mass spectroscopy coupled with photoelectron imaging. The benzene molecule was excited.to the S2 state by two 400 nm photons, and subsequently probed by one 267 nm photon. The timedependent.ion yield of the parent ion consists of two components with different lifetimes. The first.component at (90 ± 1) fs is because of internal conversion from the S2 state to the S1/S0 state. The second.one, i.e., (5.0 ± 0.2) ps, is due to decay of the S1 state. The observed lifetime of the second component is.shorter than previous results, indicating the existence of an additional decay process. With photoelectron.spectra extracted from the time-resolved photoelectron imaging, this newly found deactivated process is.assigned to intersystem crossing from the vibrational excited S1 state to the hot triplet state T3.

利用飞秒时间分辨质谱结合光电子成像技术研究了苯在S2态的超快动力学过程。苯分子被两个400 nm的光子激发到S2态，随后被一个267 nm的光子探测。母离子的时间相关离子产率由具有不同寿命的两个组分组成。第一个组分在（90±1）fs，是由于从S2态到S1/S0态的内转换。第二个组分，即（5.0±0.2）ps，是由于S1态的衰减。观察到的第二个组分的寿命比之前的结果短，这表明存在一个额外的衰减过程。通过从时间分辨光电子成像中提取的光电子能谱，这个新发现的失活过程被归为从振动激发的S1态到热三重态T3的系间窜越。