Direct Measurement of Charge Transfer Probability during Photodissociation of Few-keV OD⁺ Beam

We have measured the photodissociation of few-keV OD⁺ molecular ions into either D⁺ + O or O⁺ + D final products. The three-dimensional momentum imaging measurements of the light and massive fragments in coincidence were enabled by using an upgraded two-detector setup. In this work, we show that absorption of a single 790 or 395 nm photon excites the OD⁺ from its electronic ground state to the B ${}^3\Sigma ^{-}$ state, which dissociates to the O⁺(⁴S) + D dissociation limit. To reach the other nearly degenerate dissociation limit, D⁺ + O(³P), a unimolecular charge transfer, B ${}^3\Sigma ^{-}$ to X ${}^3\Sigma ^{-}$, transition is required following the same photoexcitation. The measured branching ratio of these dissociation channels is a direct measure of the charge transfer transition probability. This measured probability as a function of energy above the dissociation limit agrees well with our calculations.