- The mechanism of I2 dissociation in supersonic chemical oxygen-iodine lasers (COILs) is studied applying kinetic-fluid dynamics modeling, where pathways involving the excited species I2(X Σ1g+,10≤v<25), I2(X Σ1g+,25≤v≤47), I2(A′ Π32u), I2(A Π31u), O2(X Σ3g−,v), O2(a Δ1g,v), O2(b Σ1g+,v), and I(P21/2) as intermediate reactants are included. The gist of the model is adding the first reactant and reducing the contribution of the second as compared to previous models. These changes, recently suggested by Azyazov, et al. [J. Chem. Phys. 130, 104306 (2009)], significantly improve the agreement with the measurements of the gain in a low pressure supersonic COIL for all I2 flow rates that have been tested in the experiments. In particular, the lack of agreement for high I2 flow rates, which was encountered in previous models, has been eliminated in the present model. It is suggested that future modeling of the COIL operation should take into account the proposed contribution of the above mentioned reactants.