  Highly intense, sub-picosecond terahertz (THz) pulses can be used to induce
ultrafast temperature jumps (T-jumps) in liquid water. A supercritical state of
gas-like water with liquid density is established, and the accompanying
structural changes are expected to give rise to time-dependent chemical shifts.
We investigate the possibility of using extreme ultraviolet (XUV) photoelectron
spectroscopy as a probe for ultrafast dynamics induced by sub-picosecond THz
pulses of varying intensities and frequencies. To this end, we use ab initio
methods to calculate photoionization cross sections and photoelectron energies
of (H2O)$_{20}$ clusters embedded in an aqueous environment represented by
point charges. The cluster geometries are sampled from ab initio molecular
dynamics simulations modeling the THz-water interactions. We find that the
peaks in the valence photoelectron spectrum are shifted by up to 0.4 eV after
the pump pulse, and that they are broadened with respect to unheated water. The
shifts can be connected to structural changes caused by the heating, but due to
saturation effects they are not sensitive enough to serve as a thermometer for
T-jumped water.
