Radiolysis of iodine in moist air

The gas phase radiolysis of moist air, with small additions of methane and molecular iodine, has been modelled in an attempt to judge the effects of radiation fields on the chemistry of the gas phase in the containment space after a nuclear accident. The model does not allow for any interchange of species between the gas phase and liquid water, as would be the case in a real accident. Use of the currently accepted rate constants makes it clear that methyl iodide cannot be formed by abstraction of iodine atoms from I2 by methyl radicals, as sometimes assumed. The oxygen present in the air competes far too efficiently for the methyl radicals. Thus, the observed methyl iodide yields must arise in other ways. Iodine molecules were converted into oxygenated species such as IO2 and I2O3 during the first two minutes after an accident, assuming a dose rate of 2.2 x 1015 eV·dm-3·s-1. The main route for oxidation is the reaction of hydroxyl radicals with iodine molecules. This reaction has been shown to be fast, at least in the gas phase. The oxygenated iodine species are presumably converted into soluble species such as I4O9, but not enough rate constants are available to model this conversion successfully. Modelling was done with the computer program, MAKSIMA-CHEMIST. 32 refs