Selective Probing of the OH or OD Stretch Vibration in Liquid Water Using Resonant Inelastic Soft-X-Ray Scattering

Nuclear quantum effects influence the structure and dynamics of hydrogen bonded systems, such as water, which impacts their observed properties with widely varying magnitudes. This review highlights the recent significant developments in the experiment, theory and simulation of nuclear quantum effects in water. Novel experimental techniques, such as deep inelastic neutron scattering, now provide a detailed view of the role of nuclear quantum effects in water's 2 properties. These have been combined with theoretical developments such as the introduction of the competing quantum effects principle that allows the subtle interplay of water's quantum effects and their manifestation in experimental observables to be explained. We discuss how this principle has recently been used to explain the apparent dichotomy in water's isotope effects, which can range from very large to almost nonexistent depending on the property and conditions. We then review the latest major developments in simulation algorithms and theory that have enabled the efficient inclusion of nuclear quantum effects in molecular simulations, permitting their combination with on-the-fly evaluation of the potential energy surface using electronic structure theory. Finally, we identify current challenges and future opportunities in the area.3

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“…X-ray spectroscopies (71,72) (71) is thus further supported by the combined X-ray and neutron scattering data(80).…”

Section: Spectroscopic Propertiesmentioning

confidence: 62%

Nuclear Quantum Effects in Water and Aqueous Systems: Experiment, Theory, and Current Challenges

et al. 2016

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“…38,40,50 Furthermore, molecular dynamic (MD) calculations can qualitatively reproduce the fine structure without including a two component model of liquid water, rather based on ultrafast dynamics during the core-hole lifetime. 48,49 Conclusively, this would predict that the splitting in A is due to different molecular orbitals.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Probing the Hofmeister Effect with Ultrafast Core–Hole Spectroscopy

et al. 2014

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In the current work, X-ray emission spectra of aqueous solutions of different inorganic salts within the Hofmeister series are presented. The results reflect the direct interaction of the ions with the water molecules and therefore, reveal general properties of the salt−water interactions. Within the experimental precision a significant effect of the ions on the water structure has been observed but no ordering according to the structure maker/structure breaker concept could be mirrored in the results indicating that the Hofmeister effectif existentmay be caused by more complex interactions. ■ INTRODUCTIONAt the end of the 19th century, Franz Hofmeister discovered that common anions and cations could be classified according to their ability to salt in/salt out proteins, in detail to enhance aggregation and precipitation of proteins dissolved in aqueous solution; see Scheme 1. 1 By now, the so-called Hofmeister effect has been observed in a number of systems ranging from atmospheric aerosols up to whole biological entities such as cells, proteins, etc. 2,3 The salting in/out effect even plays an essential role in the metabolism of eukaryotic cells and in the case of mammalians it can lead to critical aggregation effects which were discussed as various prestages of diseases. 4,5 However, the question concerning the effect's origin remains unanswered. Two common models to explain it are (i) water interacting with the hydrated ions and causing precipitation or (ii) a consequence of the direct binding of the salt ions to the biomolecule by electrostatic interactions. 6 The first model leads to the concept of structure makers/ structure breakers (SMB), depending on the anions and cations used. According to this concept, cations and anions stabilize or destabilize the long-range water structure in aqueous solutions, 7 which is conventionally interpreted as strengthening and weakening of the hydrogen bond structure. 8 Theories based on molecular dynamic calculations have been introduced to explain the nature of the effect, some supporting the concept of structure breaking and making, 9−11 some contradicting. 12−15 However, there is a lack of understanding on the molecular level, since SMB is based on experimental observations of macroscopic properties. 16,17 Several experiments have been performed recently regarding the validation of SMB on the molecular level, which reveal objecting results. 8,18−30 Yet, the influence of salt ions on the electronic redistribution of water is unclear. In order to probe the electronic influence of salt ions on the water structure and therefore, if the SMB concept can be pictured on the molecular orbitals of the aqueous systems, corehole X-ray emission spectroscopic (XES) measurements have been performed on the oxygen K-edge of pure water and aqueous salt solutions.

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“…The so far most accurate determination of the shift and broadening of the pre-edge peak in the spectrum related to ΔZPE and ΔZPD were achieved with XRS [1,6,36]. FY-XAS of liquid H 2 O and D 2 O [26,29,37] was often analyzed alongside with investigating the x-ray emission spectrum at the O K-edge of light and heavy liquid water [1,26,27,29,34,35,37]. FY-XAS, however, suffers from well-known saturation effects which result in inaccurate determination of the spectral shape and, hence, the pre-edge peak shift and broadening cannot be accurately determined with FY-XAS.…”

Section: Introductionmentioning

confidence: 99%

“…Over the last years, x-ray spectroscopy and x-ray scattering have been used increasingly to study liquid water [1,6,[25][26][27][28][29][30][31][32][33][34][35][36][37].…”

Section: Introductionmentioning

confidence: 99%

Isotope effects in liquid water probed by transmission mode x-ray absorption spectroscopy at the oxygen K-edge

Schreck

Wernet

2016

The Journal of Chemical Physics

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The effects of isotope substitution in liquid water are probed by x-ray absorption spectroscopy at the O K-edge as measured in transmission mode. Confirming earlier x-ray Raman scattering experiments, the D 2 O spectrum is found to be blue shifted with respect to H 2 O and the D 2 O spectrum to be less broadened. Following the earlier interpretations of UV and x-ray Raman spectra, the shift is related to the difference in ground-state zero-point energies between D 2 O and H 2 O while the difference in broadening is related to the difference in ground-state vibrational zero-point distributions. We demonstrate that the transmission-mode measurements allow for determining the spectral shapes with unprecedented accuracy. Owing in addition to the increased spectral resolution and signal to noise ratio compared to the earlier measurements, the new data enable the stringent determination of blue shift and broadening in the O K-edge x-ray absorption spectrum of liquid water upon isotope substitution. The results are compared to UV absorption data and it is discussed to which extent they reflect the differences in

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Selective Probing of the OH or OD Stretch Vibration in Liquid Water Using Resonant Inelastic Soft-X-Ray Scattering

Cited by 93 publications

References 48 publications

Nuclear Quantum Effects in Water and Aqueous Systems: Experiment, Theory, and Current Challenges

Nuclear Quantum Effects in Water and Aqueous Systems: Experiment, Theory, and Current Challenges

Probing the Hofmeister Effect with Ultrafast Core–Hole Spectroscopy

Isotope effects in liquid water probed by transmission mode x-ray absorption spectroscopy at the oxygen K-edge

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