Full title: Atmospheric chemistry of dimethyl sulfide: UV spectra and self-reaction kinetics of CH₃SCH₂ and CH₃SCH₂O₂ radicals and kinetics of the reactions CH₃SCH₂ + O₂ → CH₃SCH₂O₂ and CH₃SCH₂O₂ + NO → CH₃SCH₂O + NO₂. A pulse radiolysis technique has been used to measure the UV spectra of CH₃SCH₂ and CH₃SCH₂O₂ radicals over the range 225-350 nm. At 285 nm, σ(CH₃SCH₂) = (9.8 ± 1.7) × 10^-8; at 250 nm, σ(CH₃SCH₂O₂) = (4.3 ± 0.7) × 10^-18 cm² molecule^-1. Observed self-reaction rate constants, defined as -d[CH₃SCH₂]/dt = 2k₆[CH₃SCH₂]² and -d[CH₃SCH₂O₂[/dt = 2k_7obs[CH₃SCH₂O₂]², were k₆ = (3.0 ± 0.6) × 10^-11 and k_7obs = (7.9 ± 1.4) × 10^-12 cm³ molecule^-1 s^-1. Errors are statistical (2 standard deviations) plus our estimate of potential systematic uncertainty (15%). A rate constant, k₂ = (5.7 ± 0.4) × 10^-12 cm³ molecule^-1 s^-1, was derived for the addition reaction CH₃SCH₂ + O₂ → CH₃SCH₂O₂. A rate constant, k₃ = (1.9 ± 0.6) × 10^-11 cm³ molecule^-1 s^-1, is reported for the reaction of CH₃SCH₂O₂ radicals with NO, producing NO₂. Errors for k₂ and k₃ are 2 standard deviations. Results are discussed with respect to the atmospheric chemistry of dimethyl sulfide.