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Lunkenheimer P, Emmert S, Gulich R, Köhler M, Wolf M, Schwab M, Loidl A. Electromagnetic-radiation absorption by water. Phys Rev E 2017; 96:062607. [PMID: 29347319 DOI: 10.1103/physreve.96.062607] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Indexed: 06/07/2023]
Abstract
Why does a microwave oven work? How does biological tissue absorb electromagnetic radiation? Astonishingly, we do not have a definite answer to these simple questions because the microscopic processes governing the absorption of electromagnetic waves by water are largely unclarified. This absorption can be quantified by dielectric loss spectra, which reveal a huge peak at a frequency of the exciting electric field of about 20 GHz and a gradual tailing off toward higher frequencies. The microscopic interpretation of such spectra is highly controversial and various superpositions of relaxation and resonance processes ascribed to single-molecule or molecule-cluster motions have been proposed for their analysis. By combining dielectric, microwave, THz, and far-infrared spectroscopy, here we provide nearly continuous temperature-dependent broadband spectra of water. Moreover, we find that corresponding spectra for aqueous solutions reveal the same features as pure water. However, in contrast to the latter, crystallization in these solutions can be avoided by supercooling. As different spectral contributions tend to disentangle at low temperatures, this enables us to deconvolute them when approaching the glass transition under cooling. We find that the overall spectral development, including the 20 GHz feature (employed for microwave heating), closely resembles the behavior known for common supercooled liquids. Thus water's absorption of electromagnetic waves at room temperature is not unusual but very similar to that of glass-forming liquids at elevated temperatures, deep in the low-viscosity liquid regime, and should be interpreted along similar lines.
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Affiliation(s)
- P Lunkenheimer
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - S Emmert
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - R Gulich
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - M Köhler
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - M Wolf
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - M Schwab
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - A Loidl
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
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Guarini E, Bellissima S, Bafile U, Farhi E, De Francesco A, Formisano F, Barocchi F. Density of states from mode expansion of the self-dynamic structure factor of a liquid metal. Phys Rev E 2017; 95:012141. [PMID: 28208346 DOI: 10.1103/physreve.95.012141] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Indexed: 11/07/2022]
Abstract
We show that by exploiting multi-Lorentzian fits of the self-dynamic structure factor at various wave vectors it is possible to carefully perform the Q→0 extrapolation required to determine the spectrum Z(ω) of the velocity autocorrelation function of a liquid. The smooth Q dependence of the fit parameters makes their extrapolation to Q=0 a simple procedure from which Z(ω) becomes computable, with the great advantage of solving the problems related to resolution broadening of either experimental or simulated self-spectra. Determination of a single-particle property like the spectrum of the velocity autocorrelation function turns out to be crucial to understanding the whole dynamics of the liquid. In fact, we demonstrate a clear link between the collective mode frequencies and the shape of the frequency distribution Z(ω). In the specific case considered in this work, i.e., liquid Au, analysis of Z(ω) revealed the presence, along with propagating sound waves, of lower frequency modes that were not observed before by means of dynamic structure factor measurements. By exploiting ab initio simulations for this liquid metal we could also calculate the transverse current-current correlation spectra and clearly identify the transverse nature of the above mentioned less energetic modes. Evidence of propagating transverse excitations has actually been reported in various works in the recent literature. However, in some cases, like the present one, these modes are difficult to detect in density fluctuation spectra. We show here that the analysis of the single-particle dynamics is able to unveil their presence in a very effective way. The properties here shown to characterize Z(ω), and the information in it contained therefore allow us to identify it with the density of states (DoS) of the liquid. We demonstrate that only nonhydrodynamic modes contribute to the DoS, thus establishing its purely microscopic origin. Finally, as a by-product of this work, we provide our estimate of the self-diffusion coefficient of liquid gold just above melting.
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Affiliation(s)
- E Guarini
- Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino, Italy
| | - S Bellissima
- Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino, Italy.,Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy
| | - U Bafile
- Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy
| | - E Farhi
- Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France
| | - A De Francesco
- Consiglio Nazionale delle Ricerche, Istituto Officina dei Materiali c/o Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France
| | - F Formisano
- Consiglio Nazionale delle Ricerche, Istituto Officina dei Materiali c/o Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France
| | - F Barocchi
- Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino, Italy
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Bellissima S, De Panfilis S, Bafile U, Cunsolo A, González MA, Guarini E, Formisano F. The hydrogen-bond collective dynamics in liquid methanol. Sci Rep 2016; 6:39533. [PMID: 27996056 PMCID: PMC5172242 DOI: 10.1038/srep39533] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2016] [Accepted: 11/23/2016] [Indexed: 01/21/2023] Open
Abstract
The relatively simple molecular structure of hydrogen-bonded (HB) systems is often belied by their exceptionally complex thermodynamic and microscopic behaviour. For this reason, after a thorough experimental, computational and theoretical scrutiny, the dynamics of molecules in HB systems still eludes a comprehensive understanding. Aiming at shedding some insight into this topic, we jointly used neutron Brillouin scattering and molecular dynamics simulations to probe the dynamics of a prototypical hydrogen-bonded alcohol, liquid methanol. The comparison with the most thoroughly investigated HB system, liquid water, pinpoints common behaviours of their THz microscopic dynamics, thereby providing additional information on the role of HB dynamics in these two systems. This study demonstrates that the dynamic behaviour of methanol is much richer than what so far known, and prompts us to establish striking analogies with the features of liquid and supercooled water. In particular, based on the strong differences between the structural properties of the two systems, our results suggest that the assignment of some dynamical properties to the tetrahedral character of water structure should be questioned. We finally highlight the similarities between the characteristic decay times of the time correlation function, as obtained from our data and the mean lifetime of hydrogen bond known in literature.
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Affiliation(s)
- Stefano Bellissima
- Università di Firenze, Dipartimento di Fisica, Sesto Fiorentino, I-50019, Italy
| | - Simone De Panfilis
- Istituto Italiano di Tecnologia, Center for Life Nanoscience, Roma, I-00161, Italy
| | - Ubaldo Bafile
- Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, Sesto Fiorentino, I-50019, Italy
| | - Alessandro Cunsolo
- Brookhaven National Laboratory, National Synchrotron Light Source II, Upton, New York 11973, USA
| | | | - Eleonora Guarini
- Università di Firenze, Dipartimento di Fisica, Sesto Fiorentino, I-50019, Italy
| | - Ferdinando Formisano
- Consiglio Nazionale delle Ricerche, Istituto Officina dei Materiali, Operative Group in Grenoble, F-38042, France
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