Compatibility of quantitative X-ray spectroscopy with continuous distribution models of water at ambient conditions

Abstract

The phase diagram of water harbors controversial views on underlying structural properties of its constituting molecular moieties, its fluctuating hydrogen-bonding network, as well as pair-correlation functions. In this work, long energy-range detection of the X-ray absorption allows us to unambiguously calibrate the spectra for water gas, liquid, and ice by the experimental atomic ionization cross-section. In liquid water, we extract the mean value of 1.74 ± 2.1% donated and accepted hydrogen bonds per molecule, pointing to a continuous-distribution model. In addition, resonant inelastic X-ray scattering with unprecedented energy resolution also supports continuous distribution of molecular neighborhoods within liquid water, as do X-ray emission spectra once the femtosecond scattering duration and proton dynamics in resonant X-ray–matter interaction are taken into account. Thus, X-ray spectra of liquid water in ambient conditions can be understood without a two-structure model, whereas the occurrence of nanoscale-length correlations within the continuous distribution remains open.

From atoms to aerosols: probing clusters and nanoparticles with synchrotron based mass spectrometry and X-ray spectroscopy

“…The advent of DLSRs will provide new capabilities that bridge local and global dynamics, connecting fundamental electronic, structural, and chemical dynamics with the collective phenomena of extended systems. 182 Emerging exceptionally powerful X-ray spectroscopy methods such as X-ray photon correlation spectroscopy (XPCS), 183 and resonant inelastic X-ray scattering (RIXS) 184 with sub-natural line width, as demonstrated recently to elucidate structure of water, 185 heroic at 3 rd generation light sources, should become routine at DLSRs. We seek to implement these methods at the chemical dynamics beamline.…”

Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering

“…High-resolution resonant inelastic X-ray scattering (RIXS) offers a complement to IR vibrational spectroscopy. However, how sensitive RIXS and X-ray fluorescence are to HB rearrangements, and the underlying structural implications, is a hotly debated 6–15 topic. Earlier, the long vibrational progression in quasi-elastic RIXS has been empirically analysed; Either attributed to highly weakened/broken donating HBs selected by the pre-edge core-excitation in the framework of a single bond approximation 16 .…”

“…There are competing conceptions of the local structure of liquid water; Either as a continuum of different HB configurations 21–23 , or as a mixture of two structural motifs 6,12 . Additionally, the partial contributions of different structures to the X-ray absorption (XAS) and IR spectra as well as the average number of hydrogen bonds per molecule in liquid-phase are subjects of discussion 1,15,23–26 . There is an intrinsic problem with such analyses because the relative weights of different structures are strongly dependent on the associated transition dipole moments 26 and transition energies, both of which are derived from theory, typically with limited accuracy 27 due to the large system size.…”

Nanoscale Structure in Short‐Chain Ionic Liquids

“…[31] The network resembles that of liquid water, where, however, it is formed by hydrogen bonding, and no embedded apolar domains exist. [66][67][68] While a detailed discussion of network-forming liquids is outside the scope of this paper, [69,70] we note that both water and RTILs exhibit the network's fingerprint: a closely-spaced double peak in the XRD pattern, such as the II-III peaks complex in our RTILs, and the very similar pattern shown, e. g., in Figure 2 of Ref. [67] for water.…”