Insights in the reactivity of CH2ICH2OH with OH radicals: implications for atmospheric iodine chemistry

In the case of a nuclear power plant accident, fission products may be released into the atmosphere like during the Fukushima Daichi accident. To better understand the radiological consequences of such releases, especially for iodine 131, different theoretical simulation tools were developed and used to predict its chemical atmospheric evolution. Nevertheless, significant differences have been observed between the measured and modeled atmospheric Japan concentrations of iodine 131. This can be attributed to the high reactivity of atmospheric iodine that is not fully considered in the current atmospheric dispersion codes. To address this, a new gas-phase mechanism of atmospheric iodine chemistry was developed containing 248 reactions [1]. The 0D simulation results showed a partial and rapid transformation of the gas-phase iodinated compounds (I₂, CH₃I, HOI…) into organic iodinated compounds (like short chain volatile alcohol or carboxylic acids compounds containing iodine). However, their decomposition kinetics by oxidant compounds (like atmospheric OH radical) is not known and is thus not addressed in these tools.  

The main objective of this work is to provide reliable kinetic and thermodynamic data for the gas phase reaction of CH₂ICH₂OH with the major atmospheric photooxidant, namely hydroxyl radical (OH) using high-level ab initio calculations. Several reaction pathways have been studied to assess the branching ratios between H and I atoms abstraction from CH₂ICH₂OH molecule. The structures (optimized geometries and vibrational frequencies) for all stationary points on the potential energy surface are obtained at the MP2/cc-pVTZ level of theory. The potential energies have been calculated at the DK-CCSD(T)/ANO-RCC (VTZP and VQZP) level of theory on the previous optimized geometries. The spin-orbit coupling effects have been determined using the RASSCF/CASPT2/RASSI computational protocol.

The obtained results and their implications for the modeling of iodine atmosphere chemistry will be presented and discussed in this poster.

Reference:

[1] Camille Fortin, Valérie Fèvre-Nollet, Frédéric Cousin, Patrick Lebègue, Florent Louis, Box modelling of gas-phase atmospheric iodine chemical reactivity in case of a nuclear accident, Atmospheric Environment, 214, 116838, 2019.