The ultrafast deactivation process of ethylene in the ππ∗(V) state was studied using time-resolved photoelectron imaging with sub-20 fs pulses at 159 and 198 nm. The photoelectron kinetic energy distribution observed upon 159 nm photoexcitation exhibited a continuous downward shift within 20 fs, attributed to both C-C twist and pyramidalization motions. A partial revival of the vibrational wave packet was observed with the period of about 18 fs, which is attributed to the C-C twist from 0 to 180° on the ππ∗(V) potential energy surface. Signature for internal conversion from the ππ∗(V) state to a lower-lying π3s Rydberg (R) state, which has been previously suggested, was not detected in the time-dependent photoelectron kinetic energy and angular distributions.
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