Time-resolved photoelectron spectroscopy (TRPES) is a useful approach to elucidate the coupled electronic-nuclear quantum dynamics underlying chemical processes, but has remained limited by the use of low photon energies. Here, we demonstrate the general advantages of XUV-TRPES through an application to NO2, one of the simplest species displaying the complexity of a non-adiabatic photochemical process. The high photon energy enables ionization from the entire geometrical configuration space, giving access to the true dynamics of the system. Specifically, the technique reveals dynamics through a conical intersection, large-amplitude motion and photodissociation in the electronic ground state. XUV-TRPES simultaneously projects the excited-state wave packet onto many final states, offering a multi-dimensional view of the coupled electronic and nuclear dynamics. Our interpretations are supported by ab initio wavepacket calculations on new global potential-energy surfaces. The presented results contribute to establish XUV-TRPES as a powerful technique providing a complete picture of ultrafast chemical dynamics from photoexcitation to the final products.

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Based on visible and mid-infrared transient absorption studies, probing the inter-and intraband dynamics, respectively, of magnesium phthalocyanine (MgPc) organic semiconductors, we were able to develop a model to describe the dynamics and the resulting optical response. We demonstrate how the model could offer insights into the dynamics of more complicated systems such as amorphous MgPc samples obtained by established preparation methods. In particular, we show a clear dimensionality difference of the exciton dissipation mechanism between crystalline and amorphous MgPc, which we resolve in the intraband dynamics, and how this result can also be deduced from the interband dynamics through the implementation of the developed model.

An open-loop control scheme of molecular fragmentation based on transient molecular alignment combined with single-photon ionization induced by a shortwavelength free electron laser (FEL) is demonstrated for the acetylene cation. Photoelectron spectra are recorded, complementing the ion yield measurements, to demonstrate that such control is the consequence of changes in the electronic response with molecular orientation relative to the ionizing field. We show that stable C 2 H 2 + cations are mainly produced when the molecules are parallel or nearly parallel to the FEL polarization, while the hydrogen fragmentation channel (C 2 H 2 + → C 2 H + + H) predominates when the molecule is perpendicular to that direction, thus allowing one to distinguish between the two photochemical processes. The experimental findings are supported by state-of-the art theoretical calculations.