Femtosecond Photoelectron Imaging on Pyridine: Ultrafast Electronic Dephasing from the S₁(nπ*) State and Rydberg State Energetics

Ultrafast electronic dephasing from the S 1 (nπ*) state and the energetics of the n = 3 Rydberg states of pyridine were studied by time-resolved photoelectron imaging in conjunction with (1+2‘) resonance-enhanced multiphoton ionization (REMPI) via the S 1 state. The lifetime at the S 1 origin was determined to be 32 ± 5 ps from the decay of the total photoionization signal. Photoelectron energy and angular distributions observed for (1+2‘) REMPI clearly indicated that two-photon ionization from the S 1 state is being enhanced by the resonance with singlet 3s(n -1 ) and 3p(n -1 ) Rydberg states that have not been clearly observed before. The electronic energies of the 3p x (δ=0.57) and 3p y (δ=0.50) Rydberg states were determined for the first time, to be 56 120 and 57 140 cm -1, respectively.