A photoexcited molecule undergoes a variety of photophysical and photochemical processes simultaneously or sequentially, and the molecule ultimately relaxes to the ground electronic state (S0) or further undergoes chemical reactions in S0. Time-resolved photoelectron imaging (TRPEI) enables full observation of these photoinduced dynamics, because photoionization can be induced from any part of the potential energy surfaces. However, photoionization from low-lying electronic excited states and S0 requires high probe photon energy in the vacuum ultraviolet (VUV) wavelength region, and it has been difficult to generate intense femtosecond (fs) VUV laser pulses so far. In this account, we review our effort to obtain a "global reaction map" of photoinduced dynamics of an isolated molecule by TRPEI using fs-VUV pulses. As an example, we present a full observation of cascaded radiationless transitions from the S2(ππ*) state of pyrazine (C4H4N2). Furthermore, we demonstrate that the configuration interaction of the S2(ππ*) electronic wave function can be explored by ultrafast photoionization using fs-VUV pulses. Ultrafast photodynamics of pyrazine in the VUV region are also presented.
