Experimental Study of the Reactions of Br Atoms with Thiirane and Nitrosyl Chloride

The kinetics of Br-atom reactions with C2H4S and ClNO were studied as a function of temperature at a total pressure of 2 Torr of helium using a discharge–flow system combined with mass spectrometry: Br + C2H4S → SBr + C2H4 (1) and Br + ClNO →BrCl + NO (2). The rate constant of reaction (1) was determined at T = 340–920 K by absolute measurements under pseudo-first-order conditions, either by monitoring the kinetics of Br-atom or C2H4S consumption in excess of C2H4S or of Br atoms, respectively, and by using a relative rate method: k1 = (6.6 ± 0.7) × 10−11 exp(−(2946 ± 60)/T) cm3molecule−1s−1 (where the uncertainties represent the precision at the 2σ level, the estimated total uncertainty on k1 being 15% at all temperatures). The rate coefficient of reaction (2), determined either from the kinetics of the formation of the reaction product, BrCl, or from the decays of Br-atoms in an excess of ClNO, showed non-Arrhenius behavior, being practically independent of temperature below 400 K and increasing significantly at temperatures above 500 K. The measured rate constant is well reproduced by a sum of two exponential functions: k2 = 1.2 × 10−11 exp(−19/T) + 8.0 × 10−11 exp(−1734/T) cm3 molecule−1 s−1 (with an estimated overall temperature-independent uncertainty of 15%) at T = 225–960 K.