Subpicosecond time resolved multiphoton ionization: Excited state dynamics of cis -stilbene under collision free conditions

Subpicosecond time resolved multiphoton ionization is demonstrated to be a useful technique for probing unimolecular dynamics in vapor phase samples. Vapor phase cis-stilbene molecules are observed to decay out of their initially prepared S1 state with a single exponential time constant of 0.32 ps. This decay, thought to correspond to a rapid twisting of the molecule about the ethylenic double bond, occurs in roughly one c=c double bond torsional vibrational period.