Reaction of excited iodine atoms with methyl iodide: Rate constant determinations

The rate constant for the reaction I( 2 P 1/2 ) + CH 3 I → I 2 + CH 3 has been reevaluated taking into account both collisional deactivation of excited iodine atoms and loss of I 2 by I 2 + CH 3 → I + CH 3 I. The reevaluation is based upon data obtained (R. T. Meyer), J. Chem. Phys. , 46 , 4146 (1967) from the flash photolysis of CH 3 I using time‐resolved mass spectrometry to measure the rate of I 2 formation. Computer simulations of the complete kinetic system and a closed‐form solution of a simplified set of the differential equations yielded a value of 6(± 4) × 10 6 1./mole‐sec for the excited iodine atom reaction in the temperature region of 316 to 447 K. A slight temperature dependence was observed, but an activation energy could not be evaluated quantitatively due to the small temperature range studied. An upper limit for the collisional deactivation of I( 2 P 1/2 ) with CH 3 I was also determined (2.4 × 10 7 1./mole‐sec).