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The dynamics of photo-excited 4-bromophenolate anions in aqueous solution are investigated using femtosecond extreme ultraviolet (XUV) time-resolved photoelectron spectroscopy (TRPES) in a liquid flat jet. Excitation to the first singlet... 

A setup for extreme-ultraviolet (XUV) time-resolved photoelectron spectroscopy of liquids is described based on a gas-dynamic flat jet formed by a microfluidic chip device. In comparison to a cylindrical jet that has a typical diameter of 10–30 µm, the larger surface area of the flat jet with a width of ∼300 µm allows for full overlap of the target with the pump and probe light beams. This results in an enhancement of photoelectrons emitted from the liquid while simultaneously allowing smaller sample consumption compared with other flat jet techniques utilizing liquid collisions or converging slits. Femtosecond pulses of XUV light at a photon energy of 21.7 eV are prepared by high harmonic generation and a multilayer mirror that selects a single harmonic; the He gas used to form the gas-dynamic flat jet is transparent at this energy. Compared to a cylindrical jet, the photoelectron signal from the liquid is enhanced relative to that from the surrounding vapor jacket. Pump–probe spectra for aqueous thymine show notably higher signals for the flat vs cylindrical jet. Moreover, the time-dependent space-charge shift in UV pump/XUV probe experiments is smaller for the gas-dynamic flat jet than for a cylindrical jet with the same flow rate, an effect that is accentuated at higher He backing pressures that yield a thinner jet. This reflects reduced multiphoton ionization of the solute by the UV pump pulse, the primary cause of the space charge shift, as the jet becomes thinner and reaches the thickness of a few tens of nm. 

Extreme ultraviolet (XUV) time-resolved photoelectron spectroscopy is performed for a phenolate aqueous solution in liquid flat jets. Electron detachment dynamics upon excitation to S₁and S₂states are studied. 

The photophysics of thiobases—nucleobases in which one or more oxygen atoms are replaced with sulfur atoms— vary greatly depending on the location of sulfonation. Not only are direct dynamics of a neutral thiobase impacted, but also the dynamics of excess electron accommodation. In this work, time-resolved photoelectron spectroscopy is used to measure binary anionic clusters of iodide and 4-thiouracil, I− · 4TU. We investigate charge transfer dynamics driven by excitation at 3.88 eV, corresponding to the lowest ππ* transition of the thiouracil, and at 4.16 eV, near the cluster vertical detachment energy. The photoexcited state dynamics are probed by photodetachment with 1.55 and 3.14 eV pulses. Excitation at 3.88 eV leads to a signal from a valence-bound ion only, indicating a charge accommodation mechanism that does not involve a dipole-bound anion as an intermediate. Excitation at 4.16 eV rapidly gives rise to dipole-bound and valence-bound ion signals, with a second rise in the valence-bound signal corresponding to the decay of the dipole-bound signal. The dynamics associated with the low energy ππ* excitation of 4-thiouracil provide a clear experimental proof for the importance of localized excitation and electron backfilling in halide–nucleobase clusters. 

Ultrafast UV photophysics of adenine and its derivatives are interrogated by XUV-TRPES with a gas-dynamic flat liquid jet. 

The UV-induced photo-relaxation dynamics of 5-bromouracil and 5-bromo-2′-deoxyuridine in aqueous solution were investigated using femtosecond time-resolved photoelectron spectroscopy with an extreme ultraviolet probe in a flat liquid jet.