Symmetric stretch excitation of CH3 in the 193.3 nm photolysis of CH3I

New high resolution photofragment translational spectroscopy measurements on the 193.3 nm photolysis of CH3I reveal up to four quanta of ν1 C–H symmetric stretch excitation in the C–I bond fission channel. In addition these experiments show for the first time that C–H bond fission occurs at wavelengths longer than 185 nm with a quantum yield of ∼3%. The data yields upper bounds to the C–H bond dissociation energy in CH3I of 101±1 kcal/mol and for the C–I bond energy, 55.0±0.3 kcal/mol.