New insights on the photodynamics of acetone excited with 253-288 nm femtosecond pulses

We have performed time-resolved photoelectron spectroscopy and mass spectrometry experiments to address the dynamics that result when gaseous acetone molecules are excited with femtosecond pulses in the 253-288 nm wavelength range. There are several previous examples of time-resolved mass spectrometry experiments and our results are in line with previously published data. However, the results of the photoelectron spectroscopy experiments allow us to show that the ultrafast dynamics related to the S₁ state can be attributed entirely to photo-physical processes. In essence, the dynamics that is induced by a one-photon excitation is governed by the motion out of the Franck-Condon region on the S₁ surface to the relaxed geometry in less than 30 fs. The relaxed S₁ species does not decay in 100 ps and actual C-C bond breakage must take place on a longer time scale.