Temperature-dependent kinetics studies of aqueous phase reactions of SO4− radicals with dimethylsulfoxide, dimethylsulfone, and methanesulfonate

A laser flash photolysis-long path UV-Vis absorption technique has been employed to investigate the aqueous phase reactions between the SO4− radical and three organic sulfur species of atmospheric interest, dimethylsulfoxide (DMSO; CH3S(O)CH3), dimethylsulfone (DMSO2; CH3(O)S(O)CH3), and methanesulfonate (MS; CH3(O)S(O)O−). Rate coefficients at T=298 K in units of M−1 s−1 are found to be (3.0±0.4)×109 for DMSO, <(3.9±0.5)×106 for DMSO2, and (1.1±0.3)×104 for MS (zero ionic strength limit); reported uncertainties are estimates of accuracy at the 95% confidence level. Temperature-dependent studies have been carried out over the range 278–311 K; activation energies in units of kJ mol−1 are found to be 12.0±0.4 for DMSO, 11.3±1.3 for DMSO2 and 20.7±4.3 for MS (zero ionic strength limit), where uncertainties are 2σ and represent precision only. Accuracies of rate coefficients measured at the temperature extremes of our study are thought to be similar to those reported above for the 298 K rate coefficients. The implications of the kinetics results for understanding the atmospheric sulfur cycle are discussed.