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Femtosecond time-resolved photoelectron imaging (TR-PEI) is applied to the (1 + 2‘) resonance-enhanced multiphoton ionization of pyrazine (1,4-diazabenzene) via the S1 state. The intersystem crossing (ISC) from the S1 (nπ*) to the T1 (nπ*) state and the ionization dynamics from 3s and 3pz Rydberg states are investigated. Rotational revival features, observed in the time-resolved photoelectron intensities from the T1 state populated by ISC as well as from the optically prepared S1 state, are analyzed in detail. The alignment at the rotational revival time in the T1 state is found to be much smaller than that in the S1 state. Numerical calculations, using the molecular eigenstate basis and taking account of the angular momentum coupling, to model the transfer of coherence between the S1 and T1 states are presented. The calculated time dependence of signal strength and the axis alignment are found to be in excellent agreement with the observed profiles. The diminished alignment in T1 is explained by the angu...

Femtosecond time-resolved photoelectron imaging was applied to (1+2‘) resonance-enhanced multiphoton ionization of deuterated pyrazine. The resonances with the 3s and 3p Rydberg states and rotational dephasing on a picosecond time-scale were observed similarly with pyrazine-H4. The photoionization dynamics of pyrazine-D4 was found to be identical to that of H4 at the photoionization wavelength of 393 nm. No signature was observed of the influence of the superexcited states upon ionization.

Ultrafast electronic dephasing from the S1(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 S1 state. The lifetime at the S1 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 S1 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 3px(δ=0.57) and 3py(δ=0.50) Rydberg states were determined for the first time, to be 56 120 and 57 140 cm-1, respectively.