Observation of the wavepacket dynamics on the (1)B2((1)Σ(u)(+)) state of CS2 by sub-20 fs photoelectron imaging using 159 nm probe pulses.

The wavepacket dynamics of CS2 after photoexcitation to the (1)B2((1)Σu(+)) state at 198 nm are studied by time-resolved photoelectron imaging using sub-20 fs 159 nm pulses, which enable single photon ionization from the entire region of the (1)B2 potential energy surface. The time-energy map of the photoelectron intensity reveals vibrational motions along the symmetric stretching and bending coordinates. The time-energy map of the photoelectron anisotropy parameter exhibits time-evolution within single oscillation periods of the ν1 and ν2 modes, which is attributed to variation of the excited state electronic character along these vibrational coordinates. The initially populated (1)B2 state evolves with two time constants of 107 and 394 fs.