Femtosecond
X-ray absorption spectroscopy (XAS) is a powerful method
to investigate the dynamical behavior of a system after photoabsorption
in real time. So far, the application of this technique has remained
limited to large-scale facilities, such as femtosliced synchrotrons
and free-electron lasers (FEL). In this work, we demonstrate femtosecond
time-resolved soft-X-ray absorption spectroscopy of liquid samples
by combining a sub-micrometer-thin flat liquid jet with a high-harmonic
tabletop source covering the entire water-window range (284–538
eV). Our work represents the first extension of tabletop XAS to the
oxygen edge of a chemical sample in the liquid phase. In the time
domain, our measurements resolve the gradual appearance of absorption
features below the carbon K-edge of ethanol and methanol during strong-field
ionization and trace the valence-shell ionization dynamics of the
liquid alcohols with a temporal resolution of ∼30 fs. This
technique opens unique opportunities to study molecular dynamics of
chemical systems in the liquid phase with elemental, orbital, and
site sensitivity.
Proton transfer is one of the most fundamental events in aqueous-phase chemistry and an emblematic case of coupled ultrafast electronic and structural dynamics1,2. Disentangling electronic and nuclear dynamics on the femtosecond timescales remains a formidable challenge, especially in the liquid phase, the natural environment of biochemical processes. Here we exploit the unique features of table-top water-window X-ray absorption spectroscopy3–6 to reveal femtosecond proton-transfer dynamics in ionized urea dimers in aqueous solution. Harnessing the element specificity and the site selectivity of X-ray absorption spectroscopy with the aid of ab initio quantum-mechanical and molecular-mechanics calculations, we show how, in addition to the proton transfer, the subsequent rearrangement of the urea dimer and the associated change of the electronic structure can be identified with site selectivity. These results establish the considerable potential of flat-jet, table-top X-ray absorption spectroscopy7,8 in elucidating solution-phase ultrafast dynamics in biomolecular systems.
Sub-lm thin samples are essential for spectroscopic purposes. The development of flat micro-jets enabled novel spectroscopic and scattering methods for investigating molecular systems in the liquid phase. However, the temperature of these ultra-thin liquid sheets in vacuum has not been systematically investigated. Here, we present a comprehensive temperature characterization using optical Raman spectroscopy of sub-micron flatjets produced by two different methods: colliding of two cylindrical jets and a cylindrical jet compressed by a high pressure gas. Our results reveal the dependence of the cooling rate on the material properties and the source characteristics, i.e., nozzle-orifice size, flow rate, and pressure. We show that materials with higher vapor pressures exhibit faster cooling rates, which is illustrated by comparing the temperature profiles of water and ethanol flatjets. In a sub-lm liquid sheet, the temperature of the water sample reaches around 268 K and the ethanol around 253 K close to the flatjet's terminus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.