Speaker
Description
Liquid-Jet Photoelectron Spectroscopy (LJ-PES) [1] enables the direct study of the electronic structure of both solute and solvent, and has advanced the chemical analysis in aqueous solutions. The LJ facilitates in-vacuo continuous liquid replacement, and detection of photoelectrons with minimal collisions with evaporating water molecules.
Velocity Map Imaging (VMI) [2] provides optimal photoelectron collection efficiency with a full 4π steradian range, enabling the measurement of photoelectron angular distributions (PADs) in a single image. While VMI is heavily applied to both solid and gaseous phases [3], its intriguing extension to the aqueous phase remains very challenging. Major experimental and technical difficulties include the disturbance of the focusing electric fields by the presence of the dielectric liquid jet, the background resulting from scattering of the photoelectrons with the (aqueous) solution vapor, and the balance between required high electric fields in a high-vapor environment.
We have overcome the most critical technical issues, and have successfully employed our newly developed Liquid-Jet Velocity Map Imaging (LJ-VMI) setup, comprising precisely tunable high-voltage electrodes and a microchannel plate detector. This system offers a broad dynamical energy range, allowing detection of photoelectrons kinetic energies up to approximately 40 eV. Following initial lab-experiments using laser and ultraviolet light sources, we present here our recent LJ-VMI results obtained at the bending-magnet beamline PM3, at the BESSY-II synchrotron-radiation facility. Data are presented for water, aqueous solutions, as well as non-aqueous solution. We report solute and solvent core-level and valence electron binding energies, show associated PADs, and identify the principal effects of a liquid jet in VMI performance. Next steps in our continuous development of LJ-VMI will be discussed, along the perspective for future applications towards near-ionization-threshold phenomena as well as time-resolved photo-induced reactions and electron dynamics in (aqueous) solution.
[1] B. Winter, M. Faubel, Chem. Rev., 106, 4, pp. 1176–1211, (2006)
[2] A. Eppink, D. Parker, Rev. Sci. Instrum., 68(9), pp. 3477-3484, (1997)
[3] D. M. Neumark, J. Phys. Chem. A, 127, 4207−4223, (2023)
