Photoionization study of CH3SCH2Cl formed in the reaction system Cl/Cl2/CH3SCH3

Determination of the photolysis rate coefficient of monochlorodimethyl sulfide (MClDMS) in the atmosphere and its implications for the enhancement of SO2 production from the DMS + Cl2 reaction

In this work, the photolysis rate coefficient of CH3SCH2Cl (MClDMS) in the lower atmosphere has been determined and has been used in a marine boundary layer (MBL) box model to determine the enhancement of SO2 production arising from the reaction DMS + Cl2. Absorption cross sections measured in the 28000-34000 cm(-1) region have been used to determine photolysis rate coefficients of MClDMS in the troposphere at 10 solar zenith angles (SZAs). These have been used to determine the lifetimes of MClDMS in the troposphere. At 0° SZA, a photolysis lifetime of 3-4 h has been obtained. The results show that the photolysis lifetime of MClDMS is significantly smaller than the lifetimes with respect to reaction with OH (≈ 4.6 days) and with Cl atoms (≈ 1.2 days). It has also been shown, using experimentally derived dissociation energies with supporting quantum-chemical calculations, that the dominant photodissocation route of MClDMS is dissociation of the C-S bond to give CH3S and CH2Cl. MBL box modeling calculations show that buildup of MClDMS at night from the Cl2 + DMS reaction leads to enhanced SO2 production during the day. The extra SO2 arises from photolysis of MClDMS to give CH3S and CH2Cl, followed by subsequent oxidation of CH3S.

Dynamics of the F2+CH3SCH3 reaction: A molecule-molecule reaction without entrance barrier

The F(2)+CH(3)SCH(3) reaction was studied with crossed molecular beam techniques and high level ab initio calculations. Significant reactivity was observed even at low collision energies, consistent with the negligible barrier height obtained from the ab initio calculations. All experimental findings are consistent with a weakly bound reaction intermediate of F-F-S(CH(3))(2) structure, which possesses a special type of three-center four-electron bonding. Analogous intermediates can also explain the reactions of F(2) with CH(3)SH and CH(3)SSCH(3).