  Photoexcited molecules convert photon energy into other energetic degrees of
freedom involving the coupling of ultrafast electronic and nuclear motion.
Here, we demonstrate that time-resolved x-ray photoelectron spectroscopy
(TR-XPS) offers a new way to investigate the molecular photoinduced dynamics
based on changes in the local charge at the core-probed atom. The method shows
strong sensitivity to electronic dynamics and, to a smaller extent, geometrical
changes. We demonstrate the power of TR-XPS by using sulphur
2p-core-electron-emission probing to study the UV-excited dynamics of
2-thiouracil. We identify the ultrafast Frank-Condon relaxation on the
photoexcited S2 state. The majority of the photoexcited population relaxes to
S1 and T1 states in accordance with the literature. In a second channel, 1/3 of
the population relaxes to the molecular ground state within 200 fs. In
addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS,
reveals a coherent exchange of population among electronic states.
