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 D 0 0 ( IO ) = 54.9 - 0.4 + 0.2 kcal/mol and a heat of formation 298 K of Δ H f 298 ( IO ) = 29.2 - 0.2 + 0.4 kcal/mol.