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

The wavepacket dynamics of CS₂ after photoexcitation to the ¹B₂(¹Σ_u⁺) 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 ¹B₂ 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 ¹B₂ state evolves with two time constants of 107 and 394 fs.