XUV Lasers for Ultrafast Electronic Control in H2

Abstract

Manipulation and control of molecular electron dynamics is currently in the spotlight for numerous multidisciplinary applications in physics, chemistry and biology. During the last decade, free electron lasers and sources based on high-order harmonic generation have been successfully developed to enable the generation of femtosecond and attosecond intense radiation pulses in the ultraviolet and soft X-ray regions. These tools have lead to an outbreak of pump-probe experiments suited to explore structural dynamics in atoms and molecules with spatial and temporal resolutions on the atomic length and intrinsic electronic time scales, respectively. Such experiments, using hydrogen molecules (H2, D2) as prototypical examples, have been performed to study molecular dissociative single and multi-photon ionization, photon-induced symmetry breaking in molecular dissociation, and time-resolved imaging of coherent nuclear wave-packets. The counterpart state-of-the-art time-dependent theoretical methods, able to provide a solid groundwork for describing and interpreting the underlying ultrafast physical molecular dynamics in such experiments, are still scarce. The difficulty is to achieve an accurate description accounting for the full dimensionality of the problem. A proper treatment of nuclear degrees of freedom is already indispensable to study multiphoton single ionization of diatomic molecules. This is discussed in the present manuscript in different applications. We first examine the role of the coupled electronic and nuclear motions in problems that probe coherent nuclear wave-packets using intense UV pulses and in resonance-enhanced multiphoton single ionization (REMPI) processes, whose rates are underestimated when using approaches within the fixed nuclei approximation. Later, we show that for highly intense fields the presence of vibrational structure leads to step-ladder Rabi oscillations that are probed in the REMPI probabilities. Finally, we demonstrate the suitability of these time-dependent full-dimensional treatments to provide time-resolved images of autoionization of H2, following the time evolution of both electron and proton distributions after the interaction with ultrashort pulses.