A complementary measurement method based on a home-built double-sided velocity map imaging setup is introduced. This method can simultaneously obtain time-resolved photoelectron imaging and fragment ion imaging. It has been successfully applied to investigate the ultrafast dynamics of the second singlet electronically excited state (S-2) in m-xylene. Time-resolved photoelectron and ion signals derived from the initial populated S-2 state are tracked following two-photon absorption of a pump pulse. Time-of-flight mass spectra (TOFMS) show that there are dominant parent ions and one fragment ions with methyl loss during such a process. According to the measured photoelectron images and fragment ions images, transient kinetic energy distributions and angular distributions of the generated photoelectrons and fragments are obtained and analyzed. Compared to stand-alone photoelectron imaging, the obtained fragment ion imaging is powerful for further understanding the mechanisms especially when the dissociation occurs during the pump-probe ionization. Two competing channels intersystem crossing T-3. S-2 and internal conversion S-1. S-2 are attributed to the deactivation of the S-2 state. A lifetime of similar to 50 fs for the initially excited S-2 state, of similar to 276 fs for the secondary populated S-1 state, and of 5.76 ps for the T-3 state is inferred. (C) 2016 AIP Publishing LLC.
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