Kinetic Study of the Temperature Dependence of the OH Initiated Oxidation of Dimethyl Sulphide

Abstract

The kinetics of the reaction of OH radicals with DMS have been extensively studied by a variety of direct and competitive techniques. The three early studies: two flashphotolysis/resonance fluorescence studies (in Ar/SF6 buffer gases) by Atkinson et al. (1978) and Kurylo (1978) and a competitive rate study (in 760 Torr of air) by Cox and Sheppard (1980) agreed that the rate coefficient is approximately 9 × 10 cm molecule s at ambient temperature. Atkinson et al. and Kurylo reported a small negative activation energy for the reaction. In addition, Atkinson et al. suggested that the mechanism of the reaction was a hydrogen abstraction. These three studies seemed to indicate that the rate coefficient was well defined, and unaffected by the presence of O2. However, in a later flash-photolysis/resonance fluorescence study Wine et al. (1981) obtained a rate coefficient of 4.3 × 10 cm molecule s and observed a small positive activation energy for the reaction. The authors suggested that in the previous studies, impurities in the DMS samples used may have affected the results. Also, the results of Cox and Sheppard could have been affected by secondary reactions leading to the loss of DMS. MacLeod et al. (1984) measured the rate coefficient at 373 and 573 K (no air present) and a value of 10.4 × 10 cm molecule s at room temperature was obtained from their data. They also reported a small positive activation energy. Atkinson et al. (1984) reinvestigated the reaction using a relative rate technique, and reported a rate coefficient of 10.3 × 10 cm molecule s at room temperature in the presence of 760 Torr of air. This was in reasonable agreement with Cox and Sheppard’s value in air, and the first two studies in the absence of air, but was not in agreement with the value of Wine et al. At this time, the situation was confused. But, numerous later studies: Martin et al. (1985), Wallington et al. (1986), Hynes et al. (1986), Hsu et al. (1987), Barnes et al. (1988), Nielsen et al. (1989), Abbatt et al. (1992), Hynes et al. (1995), Barone et al. (1996), and Williams et al. (2001) were carried out. The value of the activation energy was not satisfactorily resolved by these studies: Martin et al. and Wallington et al. reported small negative values for activation energy, whereas Hynes et al. (1986) and Hsu et al. reported small positive values.