Acta Phys. -Chim. Sin. ›› 2012, Vol. 28 ›› Issue (12): 2761-2766.doi: 10.3866/PKU.WHXB201210124

• THERMODYNAMICS, KINETICS, AND STRUCTURAL CHEMISTRY • Previous Articles     Next Articles

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).

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