PHOTOINDUCED PICOSECOND BIMOLECULAR REACTION BETWEEN TRANS-STILBENE AND CARBON-TETRACHLORIDE

A new photochemical reaction has been found between trans-stilbene and carbon tetrachloride. In carbon tetrachloride, the first excited sing let (S-1) state of trans-stilbene decays with a time constant of 3.1 /- 0.2 ps, a factor of ten or more faster than in alcohols and hydroca rbons. The mechanism of this anomalous lifetime shortening has been st udied by using four time-resolved spectroscopies: sub-microsecond infr ared, picosecond Raman, sub-picosecond visible absorption, and picosec ond fluorescence. After photoexcitation to the S-1 state, a bimolecula r reaction occurs between trans-stilbene and the solvent carbon tetrac hloride to form a stilbene-Cl adduct and the trichloromethyl (. CCl3) radical. Then, the stilbene-Cl adduct and the . CCl3 radical are likel y to react further in about 100 mu s, following second-order reaction kinetics. The newly found photochemical reaction between trans-stilben e and carbon tetrachloride can serve well as a prototype for studying the microscopic mechanism of bimolecular reactions in solution.