Time-resolved photoelectron spectroscopy of the allyl radical: The lifetimes of the ultraviolet bands

We report [1+1'] picosecond time-resolved pump-probe photoelectron spectra of the UV bands of the allyl radical. The experiments are performed in a molecular beam of allyl radicals, generated by supersonic jet flash pyrolysis. Photoelectron spectroscopy in a magnetic bottle is shown to be a suitable method for investigating the photophysics of organic radicals. Lifetimes were obtained for all vibronic bands between 250 and 238 nm previously assigned by MPI spectroscopy to the electronically excited B (2)A(1), C B-2(1), and D B-2(2) states, with values ranging from 20 ps to 9 ps. The nonradiative decay is due to internal conversion to the electronic ground stale. Information on the structure of the allyl cation is deduced from the photoelectron spectrum. (C) 1998 American Institute of Physics.