Tracking ultrafast relaxation dynamics of furan by femtosecond photoelectron imaging

- Relaxation dynamics of furan are tracked by femtosecond photoelectron imaging.
- The mechanism for ultrafast formation of α-carbene and β-carbene is proposed.
- Ultrafast internal conversion from S2 to S1 is observed.
- The transient characteristics of the fragment ions are obtained.
- Single-color multi-photon ionization dynamics at 800 nm are also studied.

Ultrafast internal conversion dynamics of furan has been studied by femtosecond photoelectron imaging (PEI) coupled with photofragmentation (PF) spectroscopy. Photoelectron imaging of single-color multi-photon ionization and two-color pump-probe ionization are obtained and analyzed. Photoelectron bands are assigned to the related states. The time evolution of the photoelectron signal by pump-probe ionization can be well described by a biexponential decay: two rapid relaxation pathways with time constants of ∼15 fs and 85 (±11) fs. The rapid relaxation is ascribed to the ultrafast internal conversion (IC) from the S2 state to the vibrationally hot S1 state. The second relaxation process is attributed to the redistributions and depopulation of secondarily populated high vibronic S1 state and the formation of α-carbene and β-carbene by H immigration. Additionally, the transient characteristics of the fragment ions are also measured and discussed as a complementary understanding.