The predissociation of highly excited states in acetylene by time-resolved photoelectron spectroscopy

We study the dynamics of highly excited states in acetylene initiated by an ultrashort vacuum ultraviolet laser pulse. Electronic states lying in the 4s-3d Rydberg region are excited with one femtosecond pulse, and the dynamic development of the states is monitored by a second short pulse which ionizes the system. We show that even for femtosecond pulses where the bandwidth of the exciting pulse covers several electronic states, it is possible to extract short decay lifetimes through time-resolved photoelectron spectroscopy by using a frequency-modulated (chirped) excitation pulse. We report decay lifetimes for the F 4(0)(2) and E 4-5(0)(2) states in acetylene, and for the E 4(0)(2) and E 5(0)(2) states in d-acetylene. The time evolution measured in the electron spectra is compared to decay spectra measured using ion yield and the differences in these results are discussed. (C) 2003 American Institute of Physics