Abstract The reaction CH 3 O 2+ OCl [RIGHTWARDS ARROW] prod (1) has been investigated in the temperature range 233–300 K using discharge flow mass-spectrometric technique. A rate constant k 1 (300 K)=(2.5±0.3) 10− 12 cm 3 molecule− 1 s− 1 has been obtained observing the pseudo-first-order decay of CH 3 O 2 radicals. The observed temperature dependence is described by