Ultrafast bimolecular radical reaction between S1p‐terphenyl and carbon tetrachloride: mode‐specific acceleration of vibrational dephasing in reactant molecule

Abstract

AbstractUltrafast bimolecular radical reaction proceeds between photoexcited p‐terphenyl and carbon tetrachloride. The lifetime of the first excited singlet (S1) state of p‐terphenyl in carbon tetrachloride measured with picosecond time‐resolved fluorescence spectroscopy is 5.6 ps, shorter than the typical lifetime in ordinary solvents, 0.95–2.8 ns, by a factor of 170 or more. Time‐resolved infrared spectroscopy reveals the generation of the trichloromethyl (CCl3) radical as a reaction intermediate. The decay kinetics of the CCl3 radical indicates that the CCl3 radical and the p‐terphenyl–Cl radical adduct, both of which are produced simultaneously by a radical reaction between S1p‐terphenyl and carbon tetrachloride, recombine to form the product. The picosecond time‐resolved Raman spectrum of the reactant S1p‐terphenyl shows that the dephasing process for the four vibrational modes at 1640, 1497, 1180, and 1017 cm−1 is selectively accelerated in carbon tetrachloride. The four vibrational modes probably have a large contribution from the motion of a specific atom or atoms where the intermolecular interaction that induces the bimolecular reaction is present. Copyright © 2008 John Wiley & Sons, Ltd.