Superexcited state dynamics probed with an extreme-ultraviolet free electron laser

We present the first experimental results obtained with a high-gain harmonic generation extreme ultraviolet free electron laser. The experiment probes decay dynamics of superexcited states of methyl fluoride via ion pair imaging spectroscopy. Velocity mapped ion images of the fluoride ion, obtained with excitation via intense, coherent, subpicosecond pulses of 86-89 nm radiation, reveal low translational energy, implying very high internal excitation in the methyl cation cofragment. Angular distributions show changing anisotropy as the excitation energy is tuned through this region. The dynamics underlying the dissociation are discussed with the aid of theoretical calculations.