A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of chlorine atoms with dimethyl sulfoxide (CH3S(O) CH3; DMSO) as a function of temperature (270571 K) and pressure (5-500 Torr) in nitrogen bath gas. At T = 296 K and P g 5 Torr, measured rate coefficients increase with increasing pressure. Combining our data with literature values for low-pressure rate coefficients (0.5-3 Torr He) leads to a rate coefficient for the pressure independent H-transfer channel of k(1a) = 1.45 x 10(-11) cm(3) molecule(-1) s(-1) and the following falloff parameters for the pressure-dependent addition channel in N-2 bath gas: k(1b,0) = 2.53 x 10(-28) cm(6) molecule(-2) s(-1); k(1b,infinity) = 1.17 x 10(-10) cm(3) molecule(-1) s(-1), F-c = 0.503. At the 95% confidence level, both k(1a) and k(1b)(P) have estimated accuracies of +/- 30%. At T > 430 K, where adduct decomposition is fast enough that only the H-transfer pathway is important, measured rate coefficients are independent of pressure (30-100 Torr N-2) and increase with increasing temperature. The following Arrhenius expression adequately describes the temperature dependence of the rate coefficients measured at over the range 438-571 K: k(1a) = (4.6 +/- 0.4) x 10(-11) exp[-(472 +/- 40)/T) cm(3) molecule(-1) s(-1) (uncertainties are 2 sigma, precision only). When our data at T > 430 K are combined with values for k(1a) at temperatures of 273-335 K that are obtained by correcting reported low-pressure rate coefficients from discharge flow studies to remove the contribution from the pressure-dependent channel, the following modified Arrhenius expression best describes the derived temperature dependence: k(1a) = 1.34 x 10(-15)T(1.40) exp(+ 383/T) cm(3) molecule(-1) s(-1) (273 K <= T <= 571 K). At temperatures around 330 K, reversible addition is observed, thus allowing equilibrium constants for Cl-DMSO formation and dissociation to be determined. A third-law analysis of the equilibrium data using structural information obtained from electronic structure calculations leads to the following thermochemical parameters for the association reaction: Delta H-r degrees(298) = -72.8 +/- 2.9 kJ mol(-1), Delta H degrees(0) = -71.5 +/-3.3 kJ mol(-1), and Delta S-r degrees(298) = -110.6 +/- 4.0 J K-1 mol(-1). In conjunction with standard enthalpies of formation of Cl and DMSO taken from the literature, the above values for Delta H-r lead to the following values for the standard enthalpy of formation of Cl-DMSO: Delta H-f degrees(298) = -102.7 +/- 4.9 kJ mol(-1) and Delta H-r degrees(0) = -84.4 +/- 5.8 kJ mol(-1). Uncertainties in the above thermochemical parameters represent estimated accuracy at the 95% confidence level. In agreement with one published theoretical study, electronic structure calculations using density functional theory and G3B3 theory reproduce the experimental adduct bond strength quite well.