Zero kinetic energy spectroscopy of photofragment based on ion velocity map imaging

We present the Zero Kinetic Energy spectroscopy of photoFragment (ZKEF) to determine the dissociation energy and product quantum state distributions in unimolecular photodissociation dynamics involving significant internal state excitation of photofragments. This method is based on the ion velocity map imaging (VMI) technique, by recording the photofragment signals with nearly zero kinetic energy as a function of photoexcitation energy, and thus benefits from the highest achievable energy resolution of VMI. The ZKEF spectrum directly relates to the internal energy levels of photofragments and the difference between the photoexcitation energy and the dissociation energy. Application experiments using ZKEF on the photodissociation dynamics of KrO2+ have yielded a determination of the dissociation energy of D0(Kr - O2+) = 0.222 eV, with an unprecedented accuracy of ∼1 meV. Based on this parameter, the rotational state distributions of photofragmented O2 have also been determined, demonstrating the potentials of ZKEF for high resolution characterization of photofragment quantum state distributions in photodissociation reactions.