Abstract
Angle-resolved photoemission spectroscopy of liquid water was performed using extreme ultraviolet radiation at 29.5 eV and a time-of-flight photoelectron spectrometer. SiC/Mg coated mirrors were employed to select the single-order 19th harmonic from laser high harmonics, which provided a constant photon flux for different laser polarizations. The instrument was tested by measuring photoemission anisotropy for rare gases and water molecules and applied to a microjet of an aqueous NaI solution. The solute concentration was adjusted to eliminate an electric field gradient around the microjet. The observed photoelectron spectra were analyzed considering contributions from liquid water, water vapor, and an isotropic background. The anisotropy parameters of the valence bands (1b1, 3a1, and 1b2) of liquid water are considerably smaller than those of gaseous water, which is primarily attributed to electron scattering in liquid water.
Highlights
Ultrafast spectroscopy using femtosecond lasers has revolutionized the studies of chemical reaction dynamics in atomic time- and length-scales to open a new research area of femtochemistry.1 Besides many other achievements, real-time observation of non-adiabatic dissociation of NaI by Zewail and coworkers is the landmark in this field.2 As represented by this example, photochemical reactions ubiquitously involve non-adiabatic transitions among potential energy surfaces and branching into different reaction products
Time-resolved photoelectron spectroscopy (TRPES) enables such experiments,3 if a sufficiently short probe wavelength becomes available to induce ionization from all electronic states of the reactant, transient species, and the products. Such a pulsed light source should be operated at a high repetition rate to accumulate the experimental data while limiting the number of photoelectrons generated per laser shot to avoid space charge effects
As an initial step of our effort toward extreme UV (EUV)-time and angle-resolved photoelectron spectroscopy (TARPES), we present here angle-resolved PES (ARPES) of liquid water using our EUV light source at 29.5 eV
Summary
Ultrafast spectroscopy using femtosecond lasers has revolutionized the studies of chemical reaction dynamics in atomic time- and length-scales to open a new research area of femtochemistry. Besides many other achievements, real-time observation of non-adiabatic dissociation of NaI by Zewail and coworkers is the landmark in this field. As represented by this example, photochemical reactions ubiquitously involve non-adiabatic transitions among potential energy surfaces and branching into different reaction products. Real-time observation of non-adiabatic dissociation of NaI by Zewail and coworkers is the landmark in this field.2 As represented by this example, photochemical reactions ubiquitously involve non-adiabatic transitions among potential energy surfaces and branching into different reaction products. Time-resolved photoelectron spectroscopy (TRPES) enables such experiments, if a sufficiently short probe wavelength becomes available to induce ionization from all electronic states of the reactant, transient species, and the products. Such a pulsed light source should be operated at a high repetition rate (on the order of kHz to MHz) to accumulate the experimental data while limiting the number of photoelectrons generated per laser shot to avoid space charge effects. As an initial step of our effort toward EUV-TARPES, we present here ARPES of liquid water using our EUV light source at 29.5 eV
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