Ultrafast Deactivation of the ππ*(V) State of Ethylene Studied Using Sub-20 fs Time-Resolved Photoelectron Imaging.

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.