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Kinetics and mechanism of the reaction of F atoms with CH3Br

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The reaction of F atoms with CH3Br at 296 K was studied using a pulse radiolysis/transient UV absorption spectroscopy absolute technique and a FTIR relative rate technique. The rate constant for this reaction was determined to be (4.46 ± 0.22) × 10-11. The reaction proceeds via two channels, 69 ± 5%, via hydrogen abstraction giving CH2Br radicals and HF, and 31 ± 5%, to give the adduct CH3Br-F. In the FTIR system the observed rate constant was 69 ± 8% of that measured using the pulse radiolysis system because the CH3Br-F adduct falls apart to re-form the reactants. The CH3Br-F adduct reacts with NO, with a rate constant of (2.25 ± 0.14) × 10-11 cm3 molecule-1 s-1, giving FNO as a product. There was no discernible reaction of the CH3Br-F adduct with O2 and an upper limit of 6 × 10-15 cm3 molecule-1 s-1 was derived for this reaction. The CH3Br-F adduct absorbs strongly at 260-340 nm. The absorption cross section at 280 nm of the CH3Br-F adduct was (2.06 ± 0.31) × 10-17 cm2 molecule-1. A lower limit for the equilibrium constant was [CH3Br-F]/([CH3Br][F]) > 5 × 10-16 cm3 molecule-1 at 296 K. A lower limit of 12 kcal mol-1 is estimated for the binding energy of the F atom in the CH3Br-F adduct. The UV absorption spectrum of the CH2BrO2 radical was determined; at 250 nm σ = (3.4 ± 0.9) × 10-18 cm2 molecule-1.

TidsskriftJournal of Physical Chemistry
Udgave nummer26
Sider (fra-til)10989-10998
Antal sider10
StatusUdgivet - 27 jun. 1996

ID: 225753535