Abstract
Molecular modulation spectroscopy combined with ultraviolet spectroscopic techniques have been used to observe the behavior of the CH 3 O 2 radicals generated in the gas phase by near-ultraviolet modulated photolysis of flowing Cl 2 -CH 4 -O 2 mixture. The kinetics of the disproportionation reaction (1) (1(a)) CH 3 O 2 +CH 3 O 2 →CH 3 O+CH 3 O+O 2 (1(b)) →CH 2 O+CH 3 OH+O 2 (1(c)) →CH 3 OOCH 3 +O 2 and the absorption cross-sections of CH 3 O 2 were measured by computer fitting of the modulated absorption traces obtained in the wavelength range 220 to 270 nm at 300 K and 240 torr. The rate constant for the elementary self-reaction k 1 =k 1(a) +k 1(b) +k 1(c) was determined to be (3.61±0.55)×10 −13 cm 3 molecules −1 s −1 . The parameter k obs /σ (where k obs is the observed apparent second-order rate constant) was measured from the decay curves in the dark phase of the modulated photolysis period in the wavelength range 230-260 nm, and had a value 1.16×10 5 cm s −1 at 250 nm. At 250 nm the absorption cross-section was determined as σ(CH 3 O 2 )=4.14×10 −18 cm 2 molecule −1 , leading to a value of k obs =(4.8±0.5)×10 −13 cm 3 molecule −1 s −1 . In addition, the absorption spectrum of CH 3 O 2 was measured in the range 210-295 nm using diode array spectroscopy. A detailed review of all previous studies concerning the kinetics and spectrum of the CH 3 O 2 radical is presented, and a recommended spectrum, representing an average from selected recent studies, is proposed
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