Ultrafast Photoelectron Spectroscopy of Excess Electrons in Water and Alcohols

Weyl found strong blue coloration of liquid ammonia by dissolving sodium and potassium in 1864, and it was identified later as due to an electronic transition of solvated electron. A number of theoretical and experimental studies have been reported on solvated electrons, while their structures and dynamics are not fully understood yet. We employed ultrafast photoelectron spectroscopy of liquid microjets of water, methanol and ethanol to investigate electron binding energy (eBE), electronic relaxation, and solvation dynamics of solvated electrons. Using a single order high-harmonic light source (hn = 29 eV), we refined the previously reported eBE values of solvated electrons and found the eBE distributions to be Gaussian. Using the eBE function, we developed a spectral retrieval method that enables us correct UV photoelectron spectra against electron inelastic scattering in the liquids. The excited state lifetimes of solvated electrons were measured using 3 sequential femtosecond pulses for synthesis, pump and probe. The photoelectron signals from the excited and ground state of solvated electron were clearly differentiated, and we found that non-adiabatic transition from the first excited state occurs in considerably shorter time than theoretical prediction. The solvation times in the ground state of solvated electron were extracted for the first time.
 
Ref.
Nishitani et al., Sci. Adv. 5, eaaw6896 (2019)
Karashima et al., J. Phys. Chem. Lett. 10, 4499–4504 (2019)