Discharge-flow mass spectrometric study of Cl/Cl-2/DMS and F/DMS/(Cl-2 or Br-2) chemical systems was performed at low pressure (similar to 1 Torr of helium) and 298 K. In these systems the primary organic radicals of the Cl + DMS and F + DMS reactions were titrated by reaction with Cl-2 or Br-2. It was confirmed that the reaction Cl + DMS proceeds through the unique channel Cl + CH3SCH3 --> HCl + CH3SCH2 (1a). In contrast, two channels were found for the reaction F + DMS : F + CH3SCH3 --> HF + CH3SCH2 (2a) and F + CH3SCH3 --> CH3SCH3 --> CH3 (2b) with branching ratio (2a):(2b) = 0.8:0.2. Kinetic measurements were also performed yielding the following rate constants at 298 K : F + DMS --> products (2), k(2) = (2.4 +/- 0.4) x 10(-10) cm(3) molecule(-1) s(-1); CH3SCH2 + Cl-2 --> CH3SCH2Cl + Cl (6), k(6) = (7.1 +/- 2.0) x 10(-12) cm(3) molecule(-1) s(-1). The rate constant of the reaction CH3SCH2 + CH3SCH2 + M --> (CH3SCH2)2 + M (11) was estimated, k(11) = 2.5 x 10(-11) cm(3) molecule(-1) s(-1) (P = 1 Torr of He).