We have successfully utilized noncollinear four-wave mixing in argon to generate ~160 nm femtosecond laser pulses, which can serve as the vacuum ultraviolet pump laser for time-resolved measurements. By performing a femtosecond time-resolved photoelectron imaging experiment, the ultrafast decay dynamics of pyrrole following single-photon excitation at ~160 nm is investigated. Two time constants of 50_-12^+17 and 250±50 fs are derived based on the analysis of the time-resolved photoelectron spectroscopy spectra and assigned to the excited-state lifetimes of high-lying valence and Rydberg states. In particular, the analysis of the photoelectron angular distributions clearly indicates that the initially prepared valence ππ* state (s) should be of mixed valence/Rydberg character.
Tian et al. (Thu,) studied this question.