Letter Cite This: J. Phys. Chem. Lett. 2017, 8, 5487-5491
pubs.acs.org/JPCL
Probing the OH Stretch in Different Local Environments in Liquid Water Y. Harada,*,†,‡,§ J. Miyawaki,†,‡,§ H. Niwa,†,‡,⊥ K. Yamazoe,†,§ L. G. M. Pettersson,∥ and A. Nilsson∥ †
Institute for Solid State Physics, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan Synchrotron Radiation Research Organization, The University of Tokyo, Tatsuno, Hyogo 679-5165, Japan § Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8561, Japan ∥ Department of Physics, AlbaNova University Center, Stockholm University, SE-106 91 Stockholm, Sweden ‡
ABSTRACT: We use resonant inelastic X-ray scattering (RIXS) to resolve vibrational losses corresponding to the OH stretch where the X-ray absorption process allows us to selectively probe different structural subensembles in liquid water. The results point to a unified interpretation of X-ray and vibrational spectroscopic data in line with a picture of two classes of structural environments in the liquid at ambient conditions with predominantly close-packed high-density liquid (HDL) and occasional local fluctuations into strongly tetrahedral low-density liquid (LDL).
W
X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) probe the liquid on extremely short time scales where the H-bonding network almost becomes static.10−12 These techniques involve electronic excitations and de-excitations between the O 1s core level and the unoccupied and occupied electronic states, respectively. The XAS and XES spectra show features that have been attributed to a bimodal distribution involving species with weak and distorted H-bonds or HDL and species in tetrahedral environments or LDL where the features mostly vary in terms of relative intensity but show only minor shifts with temperature.2 Vibrational spectroscopy of water has mostly focused on the OH stretch region, which in the case of isotope-substituted HDO (typically 5% HDO) makes an isolated stretch on a local OH group, giving rise to a spectral feature with a weak shoulder toward higher energy but without any fine structure.13 The spectral peak positions between simulated pure LDL and HDL phases are only on the order of 50 cm−1.14 However, when the coupling to the surrounding liquid is turned on in neat H2O (100% H2O), the spectrum becomes different due to intramolecular coupling and intermolecular coupling of resonances through H-bonds with neighboring molecules and distinct additional spectral features appear at lower energy.13,15,16
ater shows many anomalies in its thermodynamic properties, which distinguish it from a simple liquid.1 The origin of these anomalies can be related to structural fluctuations in the liquid that, contrary to simple thermal motion, increase with decreasing temperature and are correlated on specific length and time scales.1 A hypothesis to explain the anomalies is that water at high temperatures consists mainly of close-packed, rapidly fluctuating high-density liquid (HDL) local structures,1−5 also denoted normal structures that are thermally excited.6 In these HDL local structures, some hydrogen bonds (H-bonds) are strongly modified due to additional molecules at somewhat longer distances, often denoted interstitials, causing higher coordination. Hexagonal ice is the stable phase below the melting point at ambient pressure, where the water molecules are in an open, tetrahedral coordination with four strong H-bonds. Upon cooling from high temperatures, patches of tetrahedrally coordinated molecules, often denoted low-density liquid (LDL),1,7 symmetrical,8,9 or locally favored structures,6 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.1−5 It is essential to test this HDL and LDL hypothesis against various experimental measurements to determine the degree of validity of such a simple model. One of the most direct ways is to use different spectroscopic techniques to see if two classes of structural environments can be observed in water and if these show intensity variations as a function of temperature and influence of solutes. © XXXX American Chemical Society
Received: August 5, 2017 Accepted: October 11, 2017
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DOI: 10.1021/acs.jpclett.7b02060 J. Phys. Chem. Lett. 2017, 8, 5487−5491
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molecule decays back to the ground state, this will result in vibrational excitations that are comparable to what is observed in the infrared (IR) or Raman spectrum.13,27 In previous X-ray spectroscopic studies of vibrational excitations in water, the energy was tuned to the first core-excited state for which the displacement of the potential energy surface was quite large due to the antibonding character along the O−H bond. This resulted in a large number of overtones that could be detected in the vibrational spectra.21,23 Illustrated in Figure 1 are two different cases where there are different resonances in the coreexcitation process that select different H-bonded subensembles in the liquid, and subsequently, these two decay in the RIXS process into different vibrational states with distinctly different frequencies. Figure 2 shows vibrationally resolved RIXS spectra where the splitting in energy corresponds to excitations of the OH stretch.
In order to gain a deeper understanding of the liquid, it is essential that we can relate the various spectroscopies to each other. Because XES follows after XAS, they are connected through selective excitation at various XAS resonances and then denoted resonant inelastic X-ray scattering (RIXS).2,12,17 These spectral features in XAS and XES follow similar temperature dependence2 and variation with NaCl solution concentration.11,18 The question is if also the different spectral features in the neat OH stretch vibrational spectroscopy can be connected to the X-ray spectroscopies because similar trends are observed in temperature and NaCl concentration dependences between vibrational and X-ray spectroscopies.1 It has been demonstrated that it is possible to relate X-ray and vibrational spectra using high-resolution RIXS resolved as an energy-loss process from the elastic line,19−22 and OH stretch vibrational spectroscopy of water could be measured with RIXS.21,23 What we demonstrate in the present Letter is that Raman vibrational spectroscopy using soft X-rays in the RIXS process can be extended to several excitation energies in the XAS spectrum and thereby correlate the OH stretch resonances in the Raman spectrum of water with the features in the XAS spectrum for which structural assignments have been proposed. Thus, the results identify various structural environments in the liquid that give rise to the specific spectral features in the Raman spectrum. First we will establish the principle of Raman RIXS through which vibrational excitations occur. Figure 1 illustrates
Figure 2. Vibrational RIXS spectra of liquid H2O water for belowresonance, pre-edge, main-edge, and post-edge excitations.
Although we expect that bending, librations, and low-energy modes will also be excited, because the motion in these modes during the core-hole lifetime is much slower, they will not give any appreciable intensity in the RIXS spectra. With the current resolution, we therefore only see evidence of OH stretch excitations. The main peak to the right is the elastic line corresponding to the decay of the excited electron without any energy loss. The features marked ν = 1 and ν = 2 correspond to excitation of the OH stretch into, respectively, the first and second excited state. Previously it was only possible to probe the vibrational RIXS around the first core-excited state at 534− 535 eV photon energy because the excited electron in that case was strongly localized on the excited water molecule.28 The strong localization results in an enhanced cross section in the subsequent recombination decay process in comparison to when exciting at the main- or post-edge. However, with higher sensitivity, it has now become possible to study the participator decay and corresponding vibrational losses also in the decay of more highly excited and more delocalized excited states and
Figure 1. Schematic of vibrational excitations of liquid H2O water for pre-edge (selective for broken or weak H-bonds) and post-edge (selective for strong H-bonds) resonant RIXS. The blue line indicates the excitation and the orange line the de-excitation processes. Two excited-state potential energy curves are shown, and depending on the resonance of either pre-edge or post-edge excitation, one is full and the other is dashed.
excitation of a core electron to populate an unoccupied state with the same electron decaying back to fill the core-hole (participator decay) and return the system to the ground state but with loss of energy through vibrational excitations.20,21,23−25 In the core-excited state, the potential energy surface is different from that of the ground state, and because the lifetime of the O 1s core-hole state is around 4 fs,26 there is sufficient time for the vibrational wave packet to evolve along the internal O−H bond because the frequency is very high. When the core-excited 5488
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the excitation energy is much higher in the middle of the broad post-edge XAS resonance, the vibrational frequency is observed at lower energy and coincides with the second strong feature in the red region of the vibrational spectrum. We also note in this case that the overtones are significantly weaker and almost gone, which is directly related to the fact that at this high excitation energy the excited electron will delocalize on an attosecond time scale.28 The time evolution of the vibrational wave packet in the excited state thus becomes extremely limited because it is only while the excited electron is still present at the core-excited molecule that the participator decay that leads back to the ground state can occur. The OH stretch spectrum of liquid H2O has been interpreted in terms of both homogeneous and heterogeneous distributions of local structures.9,13,36 It is known that the additional lowenergy structure at 3220 cm−1 is missing in the HDO isotope decoupled spectra and is explained as essentially related to delocalized vibrations involving nearby waters strongly coupled through H-bonds.13,15,16 However, even though the vibrations are delocalized within a few shells of molecules, the electronic selectivity in the X-ray absorption process selects various subensembles for the Raman process. The connection with the XAS spectrum and thereby through selective excitation also with the XES spectra sheds more insight into the spectral assignments from a purely experimental point of view.1 The temperature dependence and NaCl solute dependence follow similar trends where the pre- and main-edge intensity, at the expense of the post-edge intensity, increases with increasing temperature and solute concentration. The same can be seen for the 3400/3630 cm−1 spectral features at the expense of the 3220 cm−1 peak. This is fully in line with the current results because the 3400/3630 cm−1 spectral features are here shown to be correlated with the pre- and main-edge XAS resonances and the 3220 cm−1 frequency region with the post-edge resonance. We can thereby use the vocabulary of HDL or a weakened or distorted H-bonded structure for the former and LDL or a tetrahedral structure for the latter, making a direct connection to the HDL−LDL fluctuation picture.1,3,37−39 The local tetrahedral structure has been shown to appear in instantaneous patches in the liquid with a characteristic size of around 1 nm from X-ray scattering at ambient conditions that grows strongly with decreasing temperature.1−5,37,40−43 This means that the coupling to other molecules through strong Hbonds in these patches will be enhanced in comparison to other local configurations with weaker H-bonds. This would explain the appearance of the 3220 cm−1 feature in neat H2O in comparison to the decoupled HDO spectra because it is mostly in the strongly H-bonded patches that this coupling would occur, and the frequency of the OH stretch of the tetrahedrally H-bonded molecules is therefore shifted to the 3220 cm−1 red region. This correlates also with the dominating spectral feature in hexagonal ice because that contains only tetrahedral structures and appears at a similar frequency.44 In this sense, it is interesting that also the post-edge in the XAS spectrum has been connected to a delocalized electronic state related to the conduction band in water through the strong H-bonds in tetrahedral structures and that this spectral feature is strongly enhanced for hexagonal ice.1,11,28,30 Thereby, the strong connection between the 3220 cm−1 and post-edge spectral features is a direct signature of strongly tetrahedral structures. The pre- and main-edge in XAS, as well as the 3400/3630 cm−1 spectral components, seem to connect well in terms of
thereby investigate various structural subensembles in the liquid that are selected through the excitation process. Figure 2 shows that the energy of the ν = 1 stretch changes with X-ray excitation energy, indicating that different H-bond environments are probed. The peak position of the ν = 1 vibrational state is extracted in terms of OH stretch energy loss and plotted in Figure 3 as a
Figure 3. Comparison between (a) vibrational energy in O 1s RIXS and (b) Raman scattering in the OH stretching region for liquid H2O water.
function of X-ray excitation energy. Here also the XAS spectrum of liquid water11 is shown in order to correlate the excitation energies with the various XAS resonances. The resulting OH stretch frequencies can be directly compared to the various parts of the optical Raman spectrum shown vertically on the right-hand side of Figure 3.29 The XAS spectrum of water shows three major spectral features in terms of the pre- (534−535 eV), main- (537−538 eV), and post-edge (540−541 eV) resonances.10,11,30 The intensity at the pre- and main-edges has been interpreted as related to weakened or distorted H-bonds, whereas the postedge is associated with strong H-bonds and is further enhanced for tetrahedral H-bond structures.8,11,30−32 It has also recently been shown that the main-edge intensity becomes enhanced upon formation of high-density forms of ice, such as highdensity amorphous (HDA) ice33 and various crystalline highpressure forms, such as ice II, VI, VII, and VIII,34 whereas the post-edge becomes stronger for hexagonal ice.10,11,30,33,35 The Raman spectrum has three clearly visible spectral features, with the main broad structure at around 3400 cm−1 denoted as the green region, a second almost as intense broad structure at 3220 cm−1 denoted as the red region, and a weak shoulder at 3630 cm−1 denoted as the blue region.29 In previous studies, these features were fitted using many different subpeaks,13,27,29 but here we only consider the clearly observable spectral structures. In Figure 3, we observe that when the X-ray excitation energy is detuned to below the onset of the main XAS spectrum the obtained vibrational frequency is found to be close to the main Raman peak at 3400 cm−1. This can be understood because far below the XAS threshold there is no selective excitation and thus all structural configurations are probed according to their statistical occurrence and we mainly detect the strongest peak that lies in the green region. However, as previously reported, when the excitation energy is increased into the pre-edge region, the vibrational frequency becomes high and is related to the blue region.21,23 Increasing the excitation energy further into the main-edge of the XAS spectrum, the frequency within the error bars becomes close to the Raman main peak of the green region. Interestingly, when 5489
DOI: 10.1021/acs.jpclett.7b02060 J. Phys. Chem. Lett. 2017, 8, 5487−5491
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The Journal of Physical Chemistry Letters temperature and solute effects. However, there is one important distinction between the two spectroscopies in that XAS probes the O atom whereas vibrational spectroscopy probes the OH bond. If there are asymmetrical structures,30,45,46 as has been proposed to be the local structure of the HDL configurations in the liquid,1−5 there can be an O atom with two distinctly different H-bonds. If the asymmetrical HDL configuration is fluctuating rapidly on a few 100 fs time scale in H-bond strength between the two OH groups,45 there can be instantaneous different local OH bonds where molecules contributing a strong pre-edge feature would give rise to the most blue-shifted part of the OH stretch spectrum.47,48 HDL configurations that are far away from the turning points in the fluctuations would contribute more to the main-edge features in the XAS and be located more in the green part of the frequency distribution in the vibrational Raman spectrum in Figure 3. Another observation from Figure 3 is that the vibrational frequencies obtained from RIXS are somewhat blue-shifted for the pre- and main-edge excited spectra in comparison to the allencompassing Raman spectrum. This can be understood if the X-ray-based vibrational frequencies come from a more strongly selected set of structural environments where the tetrahedral spectral component is missing and thereby the red-shifted spectral feature, which partly overlaps the HDL part of the Raman spectrum and slightly shifts the Raman spectral features to lower energy, is lacking. The present experimental results provide a direct connection between vibrational and X-ray spectroscopic features in liquid water. Through the electronic selectivity of the X-ray spectroscopies, the vibrational properties of specific, structurally distinct local ensembles of molecules could be determined and related to the overall Raman spectrum.
A. Nilsson: 0000-0003-1968-8696 Present Address ⊥
(H.N.) Division of Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This study was supported by the Photon and Quantum Basic Research Coordinated Development Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan. Experiments at SPring-8 BL07LSU were performed jointly by the Synchrotron Radiation Research Organization and the University of Tokyo (Proposal Nos. 2015B7403 and 2016A7401). We also acknowledge financial support from the European Research Council (ERC advanced grant WATER under Project No. 667205) and the Swedish Research Council.
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(1) Nilsson, A.; Pettersson, L. G. M. The structural origin of anomalous properties of liquid water. Nat. Commun. 2015, 6, 8998. (2) Huang, C.; Wikfeldt, K. T.; Tokushima, T.; Nordlund, D.; Harada, Y.; Bergmann, U.; Niebuhr, M.; Weiss, T. M.; Horikawa, Y.; Leetmaa, M.; et al. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 15214− 15218. (3) Stanley, H. E.; Mishima, O. The relationship between liquid, supercooled and glassy water. Nature 1998, 396, 329−335. (4) Soper, A. K.; Ricci, M. A. Structures of high-density and lowdensity water. Phys. Rev. Lett. 2000, 84, 2881−2884. (5) Bellissent-Funel, M. C. Is there a liquid-liquid phase transition in supercooled water? Europhys. Lett. 1998, 42, 161−166. (6) Russo, J.; Tanaka, H. Understanding water’s anomalies with locally favoured structures. Nat. Commun. 2014, 5, 3556. (7) Nilsson, A.; Pettersson, L. G. M. Perspective on the structure of liquid water. Chem. Phys. 2011, 389, 1−34. (8) Kühne, T. D.; Khaliullin, R. Z. Electronic signature of the instantaneous asymmetry in the first coordination shell of liquid water. Nat. Commun. 2013, 4, 1450. (9) Leetmaa, M.; Wikfeldt, K. T.; Ljungberg, M. P.; Odelius, M.; Swenson, J.; Nilsson, A.; Pettersson, L. G. M. Diffraction and IR/ Raman data do not prove tetrahedral water. J. Chem. Phys. 2008, 129, 084502. (10) Fransson, T.; Harada, Y.; Kosugi, N.; Besley, N. A.; Winter, B.; Rehr, J.; Pettersson, L. G. M.; Nilsson, A. X-ray and Electron Spectroscopy of Water. Chem. Rev. 2016, 116, 7551−7569. (11) Nilsson, A.; Nordlund, D.; Waluyo, I.; Huang, N.; Ogasawara, H.; Kaya, S.; Bergmann, U.; Näslund, L.-Å.; Ö ström, H.; Wernet, P.; Andersson, K. J.; Schiros, T.; Pettersson, L. G. M. X-ray absorption spectroscopy and X-ray Raman scattering of water; an experimental view. J. Electron Spectrosc. Relat. Phenom. 2010, 177, 99−129. (12) Nilsson, A.; Tokushima, T.; Horikawa, Y.; Harada, Y.; Ljungberg, M. P.; Shin, S.; Pettersson, L. G. M. Resonant inelastic X-ray scattering of liquid water. J. Electron Spectrosc. Relat. Phenom. 2013, 188, 84−100. (13) Bakker, H. J.; Skinner, J. L. Vibrational spectroscopy as a probe of structure and dynamics in liquid water. Chem. Rev. 2010, 110, 1498−1517. (14) Ni, Y.; Skinner, J. L. IR spectra of water droplets in no man’s land and the location of the liquid-liquid critical point. J. Chem. Phys. 2016, 145, 124509. (15) Heyden, M.; Sun, J.; Funkner, S.; Mathias, G.; Forbert, H.; Havenith, M.; Marx, D. Dissecting the THz spectrum of liquid water from first principles via correlations in time and space. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 12068−12073.
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METHODS O 1s RIXS spectra of pure liquid H2O water were collected with the HORNET station at SPring-8 BL07LSU.49 The HORNET station is equipped with a high-resolution soft X-ray RIXS spectrometer50 perpendicular to the light path of the incident X-rays. The excitation energies for the RIXS were determined by the O 1s XAS spectra recorded with partial fluorescence yield mode using a 10 mm2 silicon drift detector (SDD, Ourstex, Co. Ltd.). The energy resolution for the O 1s XAS and XES measurements was 0.1 and 0.15 eV, respectively. The water sample was purified just before the measurement using a purifier (Direct-Q, Millipore Inc., Billerica, MA, USA). A custom-made liquid flow-through cell51 was used to flush liquid water at a speed of 100 mm/s in the horizontal direction and drain from the outlet port by an aspiration pump, which corresponds to 10000/s renewal of the sample on the beam spot and is fast enough to ensure negligible radiation damage. The liquid sample was separated from the high vacuum using a thin SiC membrane with a thickness of 150 nm (NTT-AT Corporation, Japan). The irradiated area on the membrane was also changed every 4 min by 10 μm steps as a precaution. All measurements were done at room temperature.
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REFERENCES
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Y. Harada: 0000-0002-4590-9109 K. Yamazoe: 0000-0002-7249-7090 5490
DOI: 10.1021/acs.jpclett.7b02060 J. Phys. Chem. Lett. 2017, 8, 5487−5491
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The Journal of Physical Chemistry Letters (16) Nagata, Y.; Yoshimune, S.; Hsieh, C. S.; Hunger, J.; Bonn, M. Ultrafast vibrational dynamics of water disentangled by reverse nonequilibrium ab initio molecular dynamics simulations. Phys. Rev. X 2015, 5, 021002. (17) Tokushima, T.; Harada, Y.; Takahashi, O.; Senba, Y.; Ohashi, H.; Pettersson, L. G. M.; Nilsson, A.; Shin, S. High resolution X-ray emission spectroscopy of liquid water: The observation of two structural motifs. Chem. Phys. Lett. 2008, 460, 387−400. (18) Yin, Z.; Rajkovic, I.; Kubicek, K.; Quevedo, W.; Pietzsch, A.; Wernet, P.; Foehlisch, A.; Techert, S. Probing the Hofmeister effect with ultrafast core−hole spectroscopy. J. Phys. Chem. B 2014, 118, 9398−9403. (19) Couto, R. C.; Cruz, V. V.; Ertan, E.; Eckert, S.; Fondell, M.; Dantz, M.; Kennedy, B.; Schmitt, T.; Pietzsch, A.; Guimaraes, F. F.; et al. Selective gating to vibrational modes through resonant X-ray scattering. Nat. Commun. 2017, 8, 14165. (20) Hennies, F.; Pietzsch, A.; Berglund, M.; Föhlisch, A.; Schmitt, T.; Strocov, V.; Karlsson, H. O.; Andersson, J.; Rubensson, J.-E. Resonant inelastic scattering spectra of free molecules with vibrational resolution. Phys. Rev. Lett. 2010, 104, 193002. (21) Pietzsch, A.; Hennies, F.; Miedema, P. S.; Kennedy, B.; Schlappa, J.; Schmitt, T.; Strocov, V. N.; Föhlisch, A. Snapshots of the fluctuating hydrogen bond network in liquid water on the subfemtosecond timescale with vibrational resonant inelastic x-ray scattering. Phys. Rev. Lett. 2015, 114, 088302. (22) Rubensson, J. E.; Resonant inelastic soft X-ray scattering applied to molecular materials. J. Electron Spectrosc. Relat. Phenom. 2015, 200, 239−246. (23) Harada, Y.; Tokushima, T.; Horikawa, Y.; Takahashi, O.; Niwa, H.; Kobayashi, M.; Oshima, M.; Senba, Y.; Ohashi, H.; Wikfeldt, K. T.; et al. Selective probing of OH-OD stretch vibrations in liquid water using resonant inelastic soft-x-ray scattering. Phys. Rev. Lett. 2013, 111, 193001. (24) Hennies, F.; Polyutov, S.; Minkov, I.; Pietzsch, A.; Nagasono, M.; Gel’mukhanov, F.; Triguero, L.; Piancastelli, M.-N.; Wurth, W.; Ågren, H.; Föhlisch, A. Nonadiabatic effects in resonant inelastic x-ray scattering. Phys. Rev. Lett. 2005, 95, 163002. (25) Braicovich, L.; van den Brink, J.; Bisogni, V.; Moretti Sala, M.; Ament, L. J. P.; Brookes, N. B.; De Luca, G. M.; Salluzzo, M.; Schmitt, T.; Strocov, V.; Ghiringhelli, G. Magnetic Excitations and Phase Separation in the Underdoped La2−xSrxCuO4 Superconductor Measured by Resonant Inelastic X-Ray Scattering. Phys. Rev. Lett. 2010, 104, 077002. (26) Neeb, M.; Rubensson, J. E.; Biermann, M.; Eberhardt, W. Coherent excitation of vibrational wave functions observed in core hole decay spectra of O2, N2 and CO. W. J. Electron Spectrosc. Relat. Phenom. 1994, 67, 261−274. (27) Perakis, F.; De Marco, L.; Shalit, A.; Tang, F.; Kann, Z. R.; Kü hne, T. D.; Torre, R.; Bonn, M.; Nagata, Y. Vibrational Spectroscopy and Dynamics of Water. Chem. Rev. 2016, 116, 7590− 7607. (28) Nordlund, D.; Ogasawara, H.; Bluhm, H.; Takahashi, O.; Odelius, M.; Nagasono, M.; Pettersson, L. G. M.; Nilsson, A. Probing the electron delocalization in liquid water and ice at attosecond time scales. Phys. Rev. Lett. 2007, 99, 217406. (29) Sun, Q. Raman spectroscopic study of the effects of dissolved NaCl on water structure. Vib. Spectrosc. 2012, 62, 110−114. (30) Wernet, P.; Nordlund, D.; Bergmann, U.; Cavalleri, M.; Odelius, M.; Ogasawara, H.; Näslund, L. Å.; Hirsch, T. K.; Ojamäe, L.; Glatzel, P.; et al. The structure of the first coordination shell in liquid water. Science 2004, 304, 995−999. (31) Chen, W.; Wu, X.; Car, R. X-ray absorption signatures of the molecular environment in water and ice. Phys. Rev. Lett. 2010, 105, 017802. (32) Nordlund, D.; Ogasawara, H.; Andersson, K. J.; Tatarkhanov, M.; Salmerón, M.; Pettersson, L. G. M.; Nilsson, A. Sensitivity of x-ray absorption spectroscopy to hydrogen bond topology. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 80, 233404.
(33) Tse, J. S.; Shaw, D. M.; Klug, D. D.; Patchkovskii, S.; Vanko, G.; Monaco, G.; Krisch, M. X-ray raman spectroscopic study of water in the condensed phases. Phys. Rev. Lett. 2008, 100, 095502. (34) Pylkkänen, T.; Giordano, V. M.; Chervin, J.-C.; Sakko, A.; Hakala, M.; Soininen, J. A.; Hämäläinen, K.; Monaco, G.; Huotari, S. Role of non-hydrogen-bonded molecules in the oxygen K-edge spectrum of ice. J. Phys. Chem. B 2010, 114, 3804−3808. (35) Sellberg, J. A.; Kaya, S.; Segtnan, V. H.; Chen, C.; Tyliszczak, T.; Ogasawara, H.; Nordlund, D.; Pettersson, L. G. M.; Nilsson, A. Comparison of x-ray absorption spectra between water and ice: New ice data with low pre-edge absorption cross-section. J. Chem. Phys. 2014, 141, 034507. (36) Sun, Q. Local statistical interpretation for water structure. Chem. Phys. Lett. 2013, 568−569, 90−94. (37) Nilsson, A.; Huang, C.; Pettersson, L. G. M. Fluctuations in ambient water. J. Mol. Liq. 2012, 176, 2−16. (38) Poole, P. H.; Sciortino, F.; Essmann, U.; Stanley, H. E. Phase behaviour of metastable water. Nature 1992, 360, 324−328. (39) Gallo, P.; Amann-Winkel, K.; Angell, C. A.; Anisimov, M. A.; Caupin, F.; Chakravarty, C.; Lascaris, E.; Loerting, T.; Panagiotopoulos, A. Z.; Russo, J.; et al. Water: A tale of two liquids. Chem. Rev. 2016, 116, 7463−7500. (40) Huang, C.; Weiss, T. M.; Nordlund, D.; Wikfeldt, K. T.; Pettersson, L. G. M.; Nilsson, A. Increasing correlation length in bulk supercooled H2O, D2O, and NaCl solution determined from small angle x-ray scattering. J. Chem. Phys. 2010, 133, 134504. (41) Huang, C.; Wikfeldt, K. T.; Nordlund, D.; Bergmann, U.; McQueen, T.; Sellberg, J.; Pettersson, L. G. M.; Nilsson, A. Wide-angle X-ray diffraction and molecular dynamics study of medium-range order in ambient and hot water. Phys. Chem. Chem. Phys. 2011, 13, 19997−20007. (42) Overduin, S. D.; Patey, G. N. Understanding the structure factor and isothermal compressibility of ambient water in terms of local structural environments. J. Phys. Chem. B 2012, 116, 12014−12020. (43) Schlesinger, D.; Wikfeldt, K. T.; Skinner, L. B.; Benmore, C. J.; Nilsson, A.; Pettersson, L. G. M. The temperature dependence of intermediate range oxygen-oxygen correlations in liquid water. J. Chem. Phys. 2016, 145, 084503. (44) Minceva-Sukarova, B.; Sherman, W. F.; Wilkinson, G. R. The Raman spectra of ice (Ih, II, III, V, VI and IX) as functions of pressure and temperature. J. Phys. C: Solid State Phys. 1984, 17, 5833−5850. (45) Kühne, T. D.; Khaliullin, R. Z. Nature of the Asymmetry in the Hydrogen-Bond Networks of Hexagonal Ice and Liquid Water. J. Am. Chem. Soc. 2014, 136, 3395−3399. (46) Odelius, M.; Cavalleri, M.; Nilsson, A.; Pettersson, L. G. M. Xray absorption spectrum of liquid water from molecular dynamics simulations: Asymmetric model. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 024205. (47) Fecko, C. J.; Eaves, J. D.; Loparo, J. J.; Tokmakoff, A.; Geissler, P. L. Ultrafast hydrogen-bond dynamics in the infrared spectroscopy of water. Science 2003, 301, 1698−1702. (48) Fecko, C. J.; Loparo, J. J.; Roberts, S. T.; Tokmakoff, A. Local hydrogen bonding dynamics and collective reorganization in water: Ultrafast infrared spectroscopy of HOD/D2O. J. Chem. Phys. 2005, 122, 054506. (49) Yamamoto, S.; Tanaka, T.; Ohashi, H.; Hirono, T.; Kimura, H.; Fujisawa, M.; Miyawaki, J.; Harasawa, A.; Seike, T.; Takahashi, S.; et al. New soft X-ray beamline BL07LSU at SPring-8. J. Synchrotron Radiat. 2014, 21, 352−265. (50) Harada, Y.; Niwa, H.; Senba, Y.; Ohashi, H.; Tokushima, T.; Horikawa, Y.; Shin, S.; Oshima, M.; Kobayashi, Y. Ultrahigh resolution soft x-ray emission spectrometer at BL07LSU in SPring-8. Rev. Sci. Instrum. 2012, 83, 013116. (51) Tokushima, T.; Harada, Y.; Horikawa, Y.; Takahashi, O.; Senba, Y.; Ohashi, H.; Pettersson, L. G. M.; Nilsson, A.; Shin, S. High resolution X-ray emission spectroscopy of water and its assignment based on two structural motifs. J. Electron Spectrosc. Relat. Phenom. 2010, 177, 192−205.
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