FT-IR product study of the photo-oxidation of dimethyl sulfide: Temperature and O2 partial pressure dependence
作者:Cecilia Arsene,、Ian Barnes、Karl H. Becker
DOI:10.1039/a907211j
日期:——
The products of the OH-radical initiated oxidation of dimethyl sulfur (DMS) have been investigated under NOx free conditions using the photolysis of H2O2 as the OH radical source and FT-IR spectroscopy to monitor reactants and products at 1000 mbar total pressure (N2+O2). The products were investigated as a function of the temperature (284, 295 and 306±2 K) and the O2 partial pressure (20, 200 and 500 mbar). Dimethyl sulfoxide (DMSO), SO2 and methane sulfonic acid (MSA: CH3SO3H) were the major sulfur-containing products and evidence has been found for the formation of methane sulfinic acid (MSIA: CH3S(O)OH) in considerable yield. The variation of the formation of DMSO and SO2 with temperature and O2 partial pressure is consistent with a mechanism involving both addition and abstraction channels. The molar formation yields of DMSO support that a major fraction of the OH-DMS adduct formed in the addition channel reacts with O2 to form DMSO. Due to the uncertainty in the literature rate coefficients used for the corrections in the formation yield of DMSO the possibility of other channels cannot be completely excluded. High overall molar formation yields of SO2 have been measured, suggesting that further oxidation of the products in both the addition and abstraction channels result mainly in SO2 production under the NOx free conditions employed in the experiments. Consideration is made of the implications of the results for the atmospheric oxidation of DMS under conditions of low NOx such as occur in the remote marine boundary layer.
在无氮氧化物条件下,使用 H2O2 光解作为羟基自由基源,并使用傅立叶变换红外光谱监测 1000 毫巴总压(N2+O2)下的反应物和产物,研究了羟基自由基引发的二甲基硫(DMS)氧化产物。研究了产物与温度(284、295 和 306±2 K)和 O2 分压(20、200 和 500 毫巴)的函数关系。二甲基亚砜(DMSO)、二氧化硫和甲烷磺酸(MSA:CH3SO3H)是主要的含硫产物,而且有证据表明甲烷亚硫酸(MSIA:CH3S(O)OH)的生成量相当大。二甲基亚砜和二氧化硫的形成随温度和氧气分压的变化而变化,这与涉及加成和抽取通道的机理是一致的。DMSO 的摩尔形成产率证明,在加成通道中形成的 OH-DMS 加合物的大部分与 O2 反应生成 DMSO。由于用于校正二甲基亚砜形成产率的文献速率系数存在不确定性,因此不能完全排除其他途径的可能性。测得的 SO2 总摩尔形成产率很高,这表明在实验中采用的无氮氧化物条件下,加成和抽取通道中产物的进一步氧化主要导致了 SO2 的产生。研究还考虑了这些结果对二甲基亚砜在低氮氧化物条件下的大气氧化作用的影响,如在偏远的海洋边界层中发生的情况。