物理化学学报 >> 2012, Vol. 28 >> Issue (12): 2761-2766.doi: 10.3866/PKU.WHXB201210124

热力学,动力学和结构化学 上一篇    下一篇

飞秒时间分辨的光电子影像研究氯化苄分子内转换动力学

丁中华1,2, 邱学军1,2, 徐晏琪1,2, 王艳梅1,2, 张冰1,2   

  1. 1 中国科学院武汉物理与数学研究所, 波谱与原子分子物理国家重点实验室, 武汉 430071;
    2 中国科学院大学, 北京 100049
  • 收稿日期:2012-08-24 修回日期:2012-10-11 发布日期:2012-11-14
  • 通讯作者: 王艳梅 E-mail:meirwang@wipm.ac.cn
  • 基金资助:

    国家自然科学基金(21173256, 91121006)资助项目

Ultrafast Internal Conversion Dynamics of Benzyl Chloride by Femtosecond Time-Resolved Photoelectron Imaging

DING Zhong-Hua1,2, QIU Xue-Jun1,2, XU Yan-Qi1,2, WANG Yan-Mei1,2, ZHANG Bing1,2   

  1. 1 State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, Hubei 430071, P. R. China;
    2 University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2012-08-24 Revised:2012-10-11 Published:2012-11-14
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (21173256, 91121006).

摘要:

结合时间分辨的飞秒光电子影像(TRPEI)技术和时间分辨的质谱技术, 研究了氯化苄(BzCl)分子内转换动力学过程. 从光电子影像中获得了光电子动能分布和角度分布. 氯化苄分子吸收两个400 nm的光子后从基态跃迁到S4态和S2态. 获得的母体离子随泵浦-探测时间延迟变化的曲线可以用两个指数函数进行拟合, 包括一个时间常数为50 fs 的快速组分和一个时间常数为910 fs 的慢速组分. 通过分析光电子动能分布随延迟时间的变化, 我们认为分子被激发到S4态后在很短的时间内与S2态发生耦合迅速弛豫到S2态, 然后再经内转换(IC)弛豫到S1态. 最初布居的激发态分子经过内转换弛豫到S1态的时间尺度为50 fs. 910 fs 的慢速时间组分反映了分子弛豫到S1态后, 经内转换向基态S0的弛豫. 光电子角度分布的各向异性参数从零时刻的0.87增加到25fs 时的0.94, 然后逐渐减小到190 fs 时刻的0.59的现象, 也反映了氯化苄分子从S4态耦合到S2态, 然后内转换到S1态的动力学过程.

关键词: 氯化苄, 光电子影像, 内转换, 泵浦-探测, 时间分辨光谱

Abstract:

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 S4 and S2 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 τ1=50 fs and τ2=910 fs. By analysis of time-resolved photoelectron kinetic energy distributions, it is concluded that the excited S4 state has coupled with and decayed to the S2 state in a short time scale and then converted to the S1 state through ultrafast internal conversion (IC). Within 50 fs, the molecule electronically relaxes into S1 through IC and from there, decays to the S0 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 S4 state to the S2 state and the following IC to the S1 state.

Key words: Benzyl chloride, Photoelectron imaging, Internal conversion, Pump-probe, Time-resolved spectroscopy

MSC2000: 

  • O644