UC Berkeley

The combination of the liquid microjet technique and femtosecond time-resolved photoelectron spectroscopy offers a valuable means to study the electronic photoinduced dynamics of liquids and solvated species. Here, a liquid microjet formed by forcing fluid through a few micron-diameter capillary is crossed with pump and probe pulses to first excite the sample some known time before the sample is photoionized. By collecting and energy analyzing the resultant photoelectrons, the transient electronic states populated by the pump pulse can be observed and excited state population tracked as it relaxes on femtosecond to picosecond timescales.A major limitation for the study of solvated species using femtosecond photoelectron spectroscopy has been the ability to reach probe energies greater than 10 eV in a tabletop experiment. A readily accessible solution to this limitation exists in the high harmonic generation (HHG) technique, by which femtosecond pulses well in excess of 10 eV can be generated in a tabletop setup. This dissertation details the implementation of an HHG-based beamline used to generate probe pulses of 21.7 eV integrated into the liquid jet time-resolved photoelectron spectroscopy (LJ-TRPES) experiment. Previously, this project had employed UV pump/UV probe LJ-TRPES to study the excited state dynamics of solvated electrons and nucleic acid constituents (NACs). A summary of this work is given and the respective mechanisms for relaxation discussed. Additionally, the advances in tabletop light sources extending into the extreme ultraviolet (XUV) and soft x-ray regimes are discussed in the context of observation of full valence level dynamics and the potential for tracking dynamics with element specificity. Finally, the characterization and application of these new XUV probe capabilities is discussed. The XUV probe has been used to take static, pump-probe, and LAPE spectra of a variety of gas and solution phase systems, thereby demonstrating the capabilities of the technique. In particular, the observation of the ultrafast relaxation pathways in a variety of NACs is presented. The first time-resolved photoelectron spectroscopy studies using a liquid flat jet source and observation of adenine excited state relaxation using an XUV probe are notable results. These studies reveal dynamics that the experiment was previously blind to due to the probe energy limitations.