Theoretical Study of the Reactivity of Organic Iodine Compounds

Theoretical Study of the Reactivity of Organic Iodine Compounds

Dorra KHIRI

Subject
The importance of iodine in the atmosphere is known for more than two decades. Among the frequently discussed effects of atmospheric iodine are: (i) the ozone depletion in the lower stratosphere due to the presence of IO and OIO species, (ii) the role of iodine compounds in new particle formation in marine environments, (iii) chemistry of halogens in troposphere through the interaction of iodine compounds with bromides and chlorides. Besides iodomethane (CH₃I), several other organic compounds (CH₂I_2, CH₂ClI, C₂H₅I, C₃H₇I) have been detected in marine boundary layer in the coastal water or in open ocean. They participate in the generation of aerosols in coastal zones.

Alkyl iodides can undergo several decomposition pathways. For instance, CH₃I is easily photolyzed producing iodine atoms that enter ozone cycle or can react with NO, HO_2, ClO, BrO, or IO. CH₃I can abstract either H or I under attack of OH radicals, or Cl atoms, provided the concentration of the reactant radicals is high enough to compete with the photolysis. The kinetics of the reactions involving atmospheric iodine has attracted attention of experimentalists and theoreticians because reliable molecular data serve as input for global geophysical simulation models.

High-level ab initio and DFT studies offer a viable alternative to provide reliable thermodynamic and kinetic data for the gas-phase chemical reactions. Modelling is rather demanding task because for predicting the kinetic parameters one has to reach at least the chemical accuracy of the underlying thermodynamic data (better than ± 4 kJ mol-1). This implies to choose the computational chemistry tools that include all necessary and accurate corrections to molecular energies  (basis set saturation, valence and core-valence electron, correlation, relativistic effects, spin-adaptation, vibration contributions, and tunnelling corrections, …).

This project is performed in the framework of the Labex CaPPA (Chemical and Physical Properties of the Atmosphere).

Laboratory
PC2A – PhysicoChimie des Processus de Combustion et de l’Atmosphère
UMR CNRS 8522, Université de Lille 1
Bât. C11 – 59655 Villeneuve d’Ascq

Period
start: September 2016
end: September 2017

Adviser
Florent Louis (florent.louis@univ-lille1.fr)

Financing
Labex CaPPA