The 20-molecule “liquid” cluster used in the quantum-chemical computations.
Auger spectra of free water molecules, free water clusters of two sizes, and ice. The cluster spectrum marked (a) comes from smaller clusters than (b), as determined from the molecule-cluster shift in core-level PES. Molecular contributions can be seen in the cluster spectra, particularly the intense peak at . A broadened version of the molecular spectrum (dashed line), and the same spectrum shifted by (solid line) is also included in the graph (see text). The ice spectrum is reproduced from Fig. 2 in Ref. 10, and has been arbitrarily shifted in energy to coincide with the cluster spectra.
Schematic figure of the energies of one- and two-hole states in a molecule and in a cluster.
Photoelectron spectra of the O core level, including least-squares fits. Both a molecular and a cluster feature can be seen in the spectrum in the main part. In the inset, a spectrum of the water molecule is presented, to make clear the vibrational contribution to the line shape. The molecular spectrum was recorded with the same photon energy and setup as the cluster spectrum, but with expansion parameters that exclude cluster formation. The cluster spectrum was recorded under the same conditions as Auger spectrum (a) in Fig. 2.
The valence-band photoelectron spectrum of water molecules (dotted line) and clusters (solid line), recorded with photon energy, under the same conditions as cluster spectrum (a) in Fig. 2. Some molecular contribution can be seen in the cluster spectrum, and the resolution in the spectrum was determined from these sharp lines, as well as the calibration of the binding energy.
The two-hole binding energy of water clusters. The experimental spectrum is the one marked (a) in Fig. 2. Note that molecular two-hole binding energies will be higher than indicated by this scale. The boxes indicate the full widths at half maximum for convolutions of the single-hole cluster features. The B3LYP calculations for a “liquidlike” cluster give a lowest two-hole binding energy of , indicated by the bar in the graph.
The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in the liquidlike water cluster from density-functional calculations.
A comparison of experimental Auger spectra of free water molecules and water clusters with theoretical Auger spectra calculated for a water molecule and a water pentamer. The lines drawn between the spectra indicate where some of the more intense lines in the theoretical molecular Auger spectrum end up if they are stiffly shifted by three times the experimental molecule-cluster core-level shift.
Binding-energy shifts and additional broadening for cluster features relative to the molecular spectrum for the outer valence states and the core-hole state.
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