KINETICS AND MECHANISM OF THE REACTIONS OF THE SD RADICAL WITH BR2, BRCL, CL2, AND F2

Motivated by the need to improve the understanding of radical-molecule reactivity, the rate constants for the reactions of the SD radical with an interhalogen series (Br2, BrCl, Cl2, and F2) were measured as a function of temperature with a discharge-flow apparatus. The SD radical was monitored by a laser-induced fluorescence technique. The reactions were found to proceed by halogen atom abstraction with the following bimolecular rate constants (95% confidence level, in units of cm3 molecule-1 s-1): SD + Br2 --> BrSD + Br, k1 = (6.0 +/- 1.5) x 10(-11) exp[(160 +/- 100)/T] for 273 K < T < 373 K; SD + BrCl --> products, k2 = (2.3 +/- 0.3) x 10(-11) exp[(350 +/- 80)/T] for 298 K < T < 373 K; SD + BrCl --> ClSD + Br, k2b = (2.3 +/- 2) x 10(-11) exp[(100 +/- 200)/T] for 298 K < T < 373 K; SD + Cl2 --> ClSD + Cl, k3 = (1.7 +/- 0.4) x 10(-11) exp[(-690 +/- 90)/T] for 273 K < T < 373 K; SD + F2 --> FSD + F, k4 = (4.3 +/- 1.4) x 10(-11) exp[(-1390 +/- 100)/T] for 298 K < T < 373 K. We examine these results within the framework of a reactivity trend that correlates the room-temperature rate constants with the parameter (IP - EA), where IP and EA represent the ionization potential of the electron density donating reactant and the electron affinity of the electron density acceptor, respectively. It was found that the trend fails for these and other halogen atom abstraction reactions unless a correction for the effects of polarizability is included.