The lifetime of the perpendicular minimum of cis-stilbene observed by dissociative intense-laser field ionization

Cis-stilbene was excited by one photon at 270 nm in the gas phase and then probed by ionization at infrared wavelengths (810 and 2100 nm), recording the delay-time dependent mass spectra. We found not only a decay of 300 fs, previously assigned to departure from the fluorescent region, but also a second time constant (160 fs), probably representing departure from the ‘perpendicular minimum’ (excited state with twisted ethene part). In addition, two coherent oscillations (periods 140 and ≈600 fs) were found in the 300-fs window. We discuss their implications for the initial motion and point out the importance of vibronic interaction of excited states.