Abstract
There has been a discussion on the interpretation of the resonant inelastic x-ray scattering (RIXS) spectra of liquid water in terms of either different structural environments or that core hole dynamics can generate well-resolved dissociative spectral components. We have used RIXS with high resolution in the OH stretch vibration energy part, at extremely high overtones going toward the continuum of full OH bond breakage, to identify the amount of dissociative contributions in the valence band RIXS spectra at different excitation energies. We observe that at low excitation energies, corresponding to population of states with strongly antibonding character, the valence band RIXS spectra have a large contribution from a well-resolved dissociative feature. Instead, at higher excitations, this spectral component diminishes and becomes a weak structure on the high-energy side of one of the spectral peaks related to the 1b1 state from tetrahedral configurations. This result brings both interpretations to be essential for the understanding of RIXS spectra of liquid water.
Highlights
In order to explain over 70 unusual properties of water,1 it has been proposed that there are fluctuations in water at ambient conditions between two local environments that have distinctly different structures
There has been a discussion on the interpretation of the resonant inelastic x-ray scattering (RIXS) spectra of liquid water in terms of either different structural environments or that core hole dynamics can generate well-resolved dissociative spectral components
We have used RIXS with high resolution in the OH stretch vibration energy part, at extremely high overtones going toward the continuum of full OH bond breakage, to identify the amount of dissociative contributions in the valence band RIXS spectra at different excitation energies
Summary
In order to explain over 70 unusual properties of water, it has been proposed that there are fluctuations in water at ambient conditions between two local environments that have distinctly different structures. The dominating local motifs at ambient pressures have been proposed to consist mostly of close-packed, high-density liquid (HDL) local structures, denoted normal, thermally excited structures, where some hydrogen bonds (H-bonds) are strongly modified to allow higher coordination. Upon cooling from high temperatures, patches of tetrahedrally coordinated molecules, often denoted low-density liquid (LDL), symmetrical or locally favored structures, begin to appear as fluctuations in the HDL random structure. The number of such LDL patches and their size and lifetime would increase with decreasing temperature and make the properties of water deviate from the simple liquid behavior at high temperatures.. The electronic structure probe of the occupied orbitals, x-ray emission spectroscopy (XES) or often denoted resonant inelastic x-ray scattering (RIXS), shows for water that the highest occupied orbital 1b1 is split into two components 1b1′ and 1b1′′;13,14 see Fig. 1
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