Ultrafast Internal Conversion Dynamics of Benzyl Chloride by Femtosecond Time-Resolved Photoelectron Imaging
Ultrafast Internal Conversion Dynamics of Benzyl Chloride by Femtosecond Time-Resolved Photoelectron Imaging
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通过飞秒时间分辨光电子成像研究氯化苄的超快内转换动力学
DOI：
10.3866/pku.whxb201210124
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发表时间：
2012-12
期刊：
影响因子：
--
通讯作者：
Zhang Bing
中科院分区：
文献类型：
--
作者：
Qiu Xue-Jun;Xu Yan-Qi;Wang Yan-Mei;Zhang Bing
用飞秒时间分辨光电子成像(TRPEI)与时间分辨质谱联用(TRPEI)研究了氯化苄(BZCl)的超快内转化过程。从一系列光电子图像中得到了光电子强度和角各向异性的时间-能量图。在吸收两个400 nm的光子后，氯化苄同时被激发到S-4和S-2态。具有不同泵浦-探测延迟的母离子的时间演化可以用双指数衰减来很好地描述。拟合结果为T-1=50f/s，T-2=910/s。通过对时间分辨光电子动能分布的分析，认为受激发的S-4态在短时间内与S-2态耦合衰变到S-2态，然后通过超快内转换(IC)转变为S-1态。在50fs内，分子通过IC电子弛豫成S-1，然后从那里衰变到S-0基态，其时间常数相对较慢，为910fs。光电子角分布的各向异性参数从延迟时间0fs时的0.87变化到25fs时的0.94，再到190fs时的0.59，也反映了从S-4态到S-2态以及随后的IC到S-1态的耦合。
The ultrafast internal conversion of benzyl chloride (BzCl) was studied with femtosecond time-resolved photoelectron imaging (TRPEI) coupled with time-resolved mass spectroscopy. Time-energy maps of the photoelectron intensity and the angular anisotropy were generated from a series of photoelectron images. Upon absorption of two 400 nm photons, benzyl chloride was excited to the S-4 and S-2 states at the same time. The time evolution of the parent ion with different pump-probe delays can be well described by biexponential decay. The fit yielded T-1=50 fs and T-2=910 fs. By analysis of time-resolved photoelectron kinetic energy distributions, it is concluded that the excited S-4 state has coupled with and decayed to the S-2 state in a short time scale and then converted to the S-1 state through ultrafast internal conversion (IC). Within 50 fs, the molecule electronically relaxes into S-1 through IC and from there, decays to the S-0 ground state with the relatively slow time constant of 910 fs. The anisotropy parameters of photoelectron angular distributions changed from 0.87 at the delay time of 0 fs to 0.94 at 25 fs and then to 0.59 at 190 fs, which also reflects the coupling from the S-4 state to the S-2 state and the following IC to the S-1 state.