We demonstrate the capabilities of time-dependent density functional theory (TDDFT) for strong-field, short wavelength (soft X-ray) physics, as compared to a formalism based on rate equations. We find that TDDFT provides a very good description of the total and individual ionization yields for Ne and Ar atoms exposed to strong laser pulses. We assess the reliability of different adiabatic density functionals and conclude that an accurate description of long-range interactions by the exchange and correlation potential is crucial for obtaining the correct ionization yield over a wide range of intensities (10 13 -5×10 15 W/cm 2 ). Our TDDFT calculations disentangle the contribution from each ionization channel based on the Kohn-Sham wavefunctions.

Using time dependent density functional theory (TDDFT) we examine the energy, angular and timeresolved photoelectron spectra (TRPES) of ethylene in a pump-probe setup. To simulate TRPES we expose ethylene to an ultraviolet (UV) femtosecond pump pulse, followed by a time delayed extreme ultraviolet (XUV) probe pulse. Studying the photoemission spectra as a function of this delay provides us direct access to the dynamic evolution of the molecule's electronic levels. Further, by including the nuclei's motion, we provide direct chemical insight into the chemical reactivity of ethylene. These results show how angular and energy resolved TRPES could be used to directly probe electron and nucleus dynamics in molecules.

We show that additional features can emerge in the linear absorption spectra of homonuclear diatomic molecules when the ions are described quantum mechanically. In particular, the widths and energies of the peaks in the optical spectra change with the initial configuration, mass, and charge of the molecule. We introduce a model that can describe these features and we provide a quantitative analysis of the resulting peak energy shifts and width broadenings as a function of the mass.