A SPECTROKINETIC STUDY OF CH2I AND CH2IO2 RADICALS

The UV absorption spectrum and kinetics of CH2I and CH2IO2 radicals ha ve been studied in the gas-phase at 295 K using a pulse radiolysis UV absorption spectroscopic technique. UV absorption spectra of CH2I and CH2IO2 radicals were quantified in the range 220-400 nm. The spectrum of CH2I has absorption maxima at 280 nm and 337.5 nm. The absorption c ross-section for the CH2I radicals at 337.5 nm was (4.1 +/- 0.9) x 10( -18) cm2 molecule-1. The UV spectrum of CH2IO2 radicals is broad. The absorption cross-section at 370 run was (2.1 +/- 0.5) x 10(-18) cm2 mo lecule-1. The rate constant for the self reaction of CH2I radicals, k = 4 x 10(-11) cm3 molecule-1 s-1 at 1000 mbar total pressure of SF6, w as derived by kinetic modelling of experimental absorbance transients. The observed self-reaction rate constant for CH2IO2 radicals was esti mated also by modelling to k = 9 X 10(-11) cm3 molecule-1 s-1. As part of this work a rate constant of (2.0 +/- 0.3) x 10(-10) cm3 Molecule- 1 s-1 was measured for the reaction of F atoms with CH3I. The branchin g ratios of this reaction for abstraction of an I atom and a H atom we re determined to (64 +/- 6)% and (36 +/- 6)%, respectively. (C) 1994 J ohn Wiley & Sons, Inc.