Tracing ultra-fast molecular dynamics in O₂⁺ and N₂⁺ with XUV–IR pump–probe experiments

Within this thesis, molecular dynamics of diatomic molecules is studied using the XUV–IR pump–probe technique. Here, a single extreme ultraviolet (XUV) photon created by high-harmonic generation ionizes the diatomic target molecule. The initiated dynamics is probed after a variable time delay by an ultrashort (12 fs) infrared (IR) laser pulse. The 3-dimensional momenta of all charged fragments are measured using a reaction microscope. In an experiment on O2, a nuclear wave-packet oscillation is observed on the binding potential-energy curve (PEC) of the O2+(a 4Πu) electronic state. By comparing simulated results with experimental data, theoretically predicted PECs are tested. The experimental results are best reproduced if the wave packet is propagated on a Morse potential adjusted to the experimental data. This demonstrates the sensitivity of our method and its ability to predict accurate PECs from the measured wave-packet evolution. In an N2 experiment, the pump–probe delay dependent yield of stable N2++ is observed. It is interpreted as a sequential double ionization via a highly excited antibonding cationic state. The dissociation of the intermediate state is temporally resolved and can be interrupted by multi-photon ionization with the IR pulse within ≈ 15 fs after XUV ionization