Ion imaging study of IO radical photodissociation: Accurate bond dissociation energy determination

We have studied the photodissociation dynamics of expansion-cooled IO radicals at 454.9 nm, corresponding to the A2Π3/2-X2Π3/2 (1-0) bandhead, using velocity map ion imaging. The radicals were generated using a late-mixing dual-valve photolytic reactor source. Analysis of the I(2P3/2) photofragment speed distribution provides a direct determination of the ground state bond energy of D00(IO) = 54.9-0.4+0.2 kcal/mol and a heat of formation 298 K of ΔHf298(IO) = 29.2-0.2+0.4 kcal/mol.