We present the first measurement of the thermal desorption kinetics of meth
yl radicals. Neutral methyl radicals are photochemically produced within a
methyl iodide film condensed on MgO(100). A substantial fraction become tra
pped through inelastic collisions with the film and thermalize to the film
temperature prior to desorption. Novel residence time measurements are made
by comparing neutral and ion flight times in a time-of-flight spectrometer
, tin Arrhenius analysis of methyl radical residence times provides a desor
ption barrier of 2.5 +/- 0.5 kcal mol(-1) and a pre-factor of 10(10+/-1) s(
-1). (C) 2001 Elsevier Science B.V. All rights reserved.