Tracking ultrafast relaxation dynamics of furan by femtosecond photoelectron imaging

摘要

Ultrafast internal conversion dynamics of furan has been studied by femtosecond photoelectron imaging (PEI) coupled with photofragmentation (PF) spectroscopy. Photoelectron imaging of single-color multiphoton 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 similar to 15 fs and 85 (+/- 11) fs. The rapid relaxation is ascribed to the ultrafast internal conversion (IC) from the S-2 state to the vibrationally hot S-1 state. The second relaxation process is attributed to the redistributions and depopulation of secondarily populated high vibronic S-1 state and the formation of alpha-carbene and beta-carbene by H immigration. Additionally, the transient characteristics of the fragment ions are also measured and discussed as a complementary understanding. (C) 2014 Elsevier B.V. All rights reserved.