FT-IR PRODUCT STUDY ON THE OH RADICAL INITIATED OXIDATION OF DIMETHYL SULFIDE: TEMPERATURE AND O2 PARTIAL PRESSURE DEPENDENCE

The products of the OH radical initiated oxidation of dimethyl sulfide (DMS) have been investigated under NOx-firee conditions using the photolysis of H2O2 as the OH radical source and FT-IR spectroscopy to monitor reactants and products. The experiments were performed at five different temperatures (260, 270, 280, 290 and 298 K), at three different O-2 partial pressure (similar to 0, 205 and 500 mbar) and at a total pressure of 1,000 mbar diluent gas (N-2, synthetic air or N-2/O-2 mixture). The major sulfur-containing products were dimethyl sulfoxide (DMSO) and sulfur dioxide (SO2). As minor sulfur-containing products dimethyl sulfone (DMSO2), methyl thiol formate (MTF) and carbonyl sulfide (OCS) have been identified; the formation of trace amounts of methane sulfonic acid (MSA) were also observed. The variation of the product yields with temperature and O-2 partial pressure is consistent with the occurrence of both addition and abstraction channels in the OH radical initiated oxidation of DMS. The molar formation yields of DMSO support that a major fraction of the DMS-OH adduct formed in the addition channel reacts with O-2 to form DMSO.