Ultrafast Dynamics of Ozone Exposed to Ionizing Radiation

By irradiating ozone molecules with few-femtosecond soft x-ray pulses and probing the fragmentation pathways, we find that any excess energy is rapidly and efficiently transferred into internal excitation of the triatomic molecule. We explore the Coulomb explosion of O$_{3}$ when irradiated with soft x-rays above the double ionization threshold, at photon energies in the XUV (43 eV) range. The super-excited states are then probed using a femtosecond infrared (IR) pulse in combination with 3D coincidence momentum imaging (COLTRIMS). By comparing the O$_{3}^{+}$ and O$_{2}^{+}$ ion fragmentation yields and their kinetic energies as a function of time delay between the XUV pump and IR probe, we find that the triatomic ozone molecule shows an ability to absorb any excess energy internally rather than emerging as kinetic energy released by the Coulomb exploding fragments. This internal conversion of energy in a triatomic molecule before explosion is very different from the case of diatomic molecular oxygen.