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Toraille L, Weck G, Geneste G, Pépin C, Garbarino G, Loubeyre P. Ethane under pressure revisited using x-ray diffraction, Raman spectroscopy, infrared absorption, and ab initio calculations up to 150 GPa. J Chem Phys 2024; 160:214702. [PMID: 38828824 DOI: 10.1063/5.0212117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Accepted: 05/16/2024] [Indexed: 06/05/2024] Open
Abstract
Ethane (C2H6) is anticipated to be the most stable compound within the carbon-hydrogen system under the 100 GPa pressure range. Nevertheless, the properties of ethane under pressure are still poorly documented. Here, we present a comprehensive study of the structural and vibrational properties of C2H6 in a diamond anvil cell at pressures up to 150 GPa. To obtain detailed data, ethane single-crystal was grown in a helium pressure-transmitting medium. Utilizing single-crystal x-ray diffraction, the distortion mechanism between the tetragonal and monoclinic phases, occurring over the 3.2-5.2 GPa pressure range, is disclosed. Subsequently, no phase transition is observed up to 150 GPa. The accurately measured compression curve is compared to various computational approximations. The vibrational modes measured by Raman spectroscopy and infrared absorption are well identified, and their evolution is well reproduced by ab initio calculations. In particular, an unusual anticrossing phenomenon occurs near 40 GPa between a rocking and a stretching mode, likely attributable to intermolecular interactions through hydrogen bonding.
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Affiliation(s)
- Loïc Toraille
- CEA DAM, DIF, F-91297 Arpajon, France
- Université Paris-Saclay, CEA, Laboratoire Matière en Conditions Extrêmes, 91680 Bruyères-le-Châtel, France
| | - Gunnar Weck
- CEA DAM, DIF, F-91297 Arpajon, France
- Université Paris-Saclay, CEA, Laboratoire Matière en Conditions Extrêmes, 91680 Bruyères-le-Châtel, France
| | - Grégory Geneste
- CEA DAM, DIF, F-91297 Arpajon, France
- Université Paris-Saclay, CEA, Laboratoire Matière en Conditions Extrêmes, 91680 Bruyères-le-Châtel, France
| | - Charles Pépin
- CEA DAM, DIF, F-91297 Arpajon, France
- Université Paris-Saclay, CEA, Laboratoire Matière en Conditions Extrêmes, 91680 Bruyères-le-Châtel, France
| | - Gaston Garbarino
- ESRF, The European Synchrotron, 71 Avenue des Martyrs, CS40220, 38043 Grenoble Cedex 9, France
| | - Paul Loubeyre
- CEA DAM, DIF, F-91297 Arpajon, France
- Université Paris-Saclay, CEA, Laboratoire Matière en Conditions Extrêmes, 91680 Bruyères-le-Châtel, France
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2
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Pipich V, Kohlbrecher J, Schwahn D. Thermal Density Fluctuations and Polymorphic Phase Transitions of Ethane (C 2D 6) in the Gas/Liquid and Supercritical States. J Phys Chem B 2024; 128:5072-5082. [PMID: 38747367 PMCID: PMC11129177 DOI: 10.1021/acs.jpcb.4c01422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Revised: 05/02/2024] [Accepted: 05/03/2024] [Indexed: 05/24/2024]
Abstract
The phase behavior of the liquid C2D6 below and above the critical point was investigated using small-angle neutron scattering (SANS) in temperature and pressure ranges from 10 to 45 °C and 20 to 126 bar, respectively. The scattering of thermal fluctuations of the molecular density was determined and thus the gas-liquid and Widom lines. At the same time, we observed additional scattering of droplets of more densely packed C2D6 molecules above the gas-liquid line and in the supercritical fluid regime from just below the critical point for all temperatures at about ΔP = 10 bar above the Widom line. This line is interpreted as the Frenkel line. These results are consistent with our previous studies on CO2 and thus indicate a universal phase behavior for monomolecular liquids below and above the critical point. The interpretation of the Frenkel line as the lower limit of a polymorphic phase transition is in contrast to the usual interpretation as the limit of a dynamic process. The correlation lengths (ξ) of the thermal density fluctuations at the critical point and at the Widom line are determined between 20 and 35 Å and thus in the range of the droplet radius between 60 and 80 Å. These long-range fluctuations appear to suppress the formation of droplets, which can only form at about 10 bar above the critical point and the Widom line when ξ becomes smaller than 10 Å.
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Affiliation(s)
- Vitaliy Pipich
- Jülich
Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz-Zentrum
(MLZ), Forschungszentrum Jülich GmbH, Garching D-85747, Germany
| | - Joachim Kohlbrecher
- Laboratory
for Neutron Scattering, Paul-Scherrer Institute, Villigen CH-5232 PSI, Switzerland
| | - Dietmar Schwahn
- Forschungszentrum
Jülich GmbH, Jülich Centre for Neutron Science (JCNS-1), Wilhelm-Johnen-Straße, Jülich D-52428, Germany
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3
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Pruteanu CG, Loveday JS, Ackland GJ, Proctor JE. Krypton and the Fundamental Flaw of the Lennard-Jones Potential. J Phys Chem Lett 2022; 13:8284-8289. [PMID: 36036981 PMCID: PMC9465677 DOI: 10.1021/acs.jpclett.2c02004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Accepted: 08/22/2022] [Indexed: 06/15/2023]
Abstract
We have performed a series of neutron scattering experiments on supercritical krypton. Our data and analysis allow us to characterize the Frenkel line crossover in this model monatomic fluid. The data from our measurements was analyzed using Empirical Potential Structure Refinement to determine the short- and medium-range structure of the fluids. We find evidence for several shells of neighbors which form approximately concentric rings of density about each atom. The ratio of second to first shell radius is significantly larger than in any crystal structure. Modeling krypton using a Lennard-Jones potential is shown to give significant errors, notably that the liquid is overstructured. The true potential appears to be longer ranged and with a softer core than the 6-12 powerlaws permit.
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Affiliation(s)
- Ciprian G. Pruteanu
- SUPA,
School of Physics and Astronomy and Centre for Science at Extreme
Conditions, The University of Edinburgh, Edinburgh EH9 3FD, U.K.
| | - John S. Loveday
- SUPA,
School of Physics and Astronomy and Centre for Science at Extreme
Conditions, The University of Edinburgh, Edinburgh EH9 3FD, U.K.
| | - Graeme J. Ackland
- SUPA,
School of Physics and Astronomy and Centre for Science at Extreme
Conditions, The University of Edinburgh, Edinburgh EH9 3FD, U.K.
| | - John E. Proctor
- Materials
& Physics Research Group, Newton Building, University of Salford, Manchester M5 4WT, U.K.
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4
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Pruteanu CG, Kirsz M, Ackland GJ. Frenkel Line in Nitrogen Terminates at the Triple Point. J Phys Chem Lett 2021; 12:11609-11615. [PMID: 34812632 DOI: 10.1021/acs.jpclett.1c03206] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Recent studies on supercritical nitrogen revealed clear changes in structural markers and dynamical properties when the coordination number approaches its maximum value. The line in P and T space where these changes occur is referred to as the Frenkel line. Here, we qualitatively reproduce such changes in the supercritical regime using the popular "optimized potential for liquid simulation" (OPLS) classical force field for molecular dynamics. Unfortunately, at 160 K, OPLS nitrogen predicts sublimation rather than producing a liquid phase; therefore, we developed our own force field to achieve quantitative agreement with experimental data. We confirm the asymptotic behavior of the coordination number on crossing the Frenkel line and note an associated change in the diffusion constant, consistent with the non-rigid to rigid liquid-like character of the "transition". The simulations allow us to track the Frenkel line to subcritical temperatures and demonstrate that it terminates at the triple point. This establishes the experimentally measurable changes, which could unequivocally determine the Frenkel line in other systems.
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Affiliation(s)
- Ciprian G Pruteanu
- Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
| | - Marcin Kirsz
- Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
| | - Graeme J Ackland
- Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
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5
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Cockrell C, Brazhkin VV, Trachenko K. Universal interrelation between dynamics and thermodynamics and a dynamically driven "c" transition in fluids. Phys Rev E 2021; 104:034108. [PMID: 34654136 DOI: 10.1103/physreve.104.034108] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Accepted: 08/26/2021] [Indexed: 06/13/2023]
Abstract
Our very wide survey of the supercritical phase diagram and its key properties reveals a universal interrelation between dynamics and thermodynamics and an unambiguous transition between liquidlike and gaslike states. This is seen in the master plot showing a collapse of the data representing the dependence of specific heat on key dynamical parameters in the system for many different paths on the phase diagram. As a result, the observed transition is path independent. We call it a "c" transition due to the c-shaped curve parametrizing the dependence of the specific heat on key dynamical parameters. The c transition has a fixed inversion point and provides a new structure to the phase diagram, operating deep in the supercritical state (up to, at least, 2000 times the critical pressure and 50 times the critical temperature). The data collapse and path independence as well as the existence of a special inversion point on the phase diagram are indicative of either of a sharp crossover or a new phase transition in the deeply supercritical state.
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Affiliation(s)
- C Cockrell
- School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, United Kingdom
| | - V V Brazhkin
- Institute for High Pressure Physics, RAS, 108840 Troitsk, Moscow, Russia
| | - K Trachenko
- School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, United Kingdom
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Pruteanu CG, Proctor JE, Alderman OLG, Loveday JS. Structural Markers of the Frenkel Line in the Proximity of Widom Lines. J Phys Chem B 2021; 125:8902-8906. [PMID: 34324365 DOI: 10.1021/acs.jpcb.1c04690] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have performed a neutron scattering experiment on supercritical fluid nitrogen at 160 K (1.27 TC) over a wide pressure range (7.8 MPa/0.260 g/mL-125 MPa/0.805 g/mL). This has enabled us to study the process by which nitrogen changes from a fluid that exhibits gaslike behavior to one that exhibits rigid liquidlike behavior at a temperature close to, but above, the critical temperature by crossing the Widom lines followed by the Frenkel line on pressure (density) increase. We find that the Frenkel line transition is indicated by a transition to a regime of rigid liquidlike behavior in which the coordination number remains constant within error, in agreement with our previous work at 300 K. The Frenkel line transition takes place at approximately the same density at 160 and 300 K. The data do not conclusively show an additional transition at the location of the known Widom lines. We find that behavior remains gaslike until the Frenkel line is crossed and our data support the hypothesis that Widom line transitions are density increase-driven.
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Affiliation(s)
- Ciprian G Pruteanu
- Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom.,SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
| | - John E Proctor
- Materials and Physics Research Group, Newton Building, University of Salford, Manchester M5 4WT, United Kingdom
| | - Oliver L G Alderman
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom
| | - John S Loveday
- SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
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Proctor JE, Pruteanu CG, Morrison I, Crowe IF, Loveday JS. Transition from Gas-like to Liquid-like Behavior in Supercritical N 2. J Phys Chem Lett 2019; 10:6584-6589. [PMID: 31604009 DOI: 10.1021/acs.jpclett.9b02358] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We have studied in detail the transition from gas-like to rigid liquid-like behavior in supercritical N2 at 300 K (2.4 TC). Our study combines neutron diffraction and Raman spectroscopy with ab initio molecular dynamics simulations. We observe a narrow transition from gas-like to rigid liquid-like behavior at ca. 150 MPa, which we associate with the Frenkel line. Our findings allow us to reliably characterize the Frenkel line using both diffraction and spectroscopy methods, backed up by simulation, for the same substance. We clearly lay out what parameters change, and what parameters do not change, when the Frenkel line is crossed.
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Affiliation(s)
- J E Proctor
- Materials and Physics Research Group , University of Salford , Manchester M5 4WT , U.K
| | - C G Pruteanu
- Department of Physics and Astronomy , University College London , Gower Street , London WC1E 6BT , U.K
| | - I Morrison
- Materials and Physics Research Group , University of Salford , Manchester M5 4WT , U.K
| | - I F Crowe
- Photon Science Institute and School of Electrical and Electronic Engineering , University of Manchester , Oxford Road , Manchester M13 9PL , U.K
| | - J S Loveday
- SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions , The University of Edinburgh , Edinburgh EH9 3JZ , U.K
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Kryuchkov NP, Mistryukova LA, Brazhkin VV, Yurchenko SO. Excitation spectra in fluids: How to analyze them properly. Sci Rep 2019; 9:10483. [PMID: 31324848 PMCID: PMC6642218 DOI: 10.1038/s41598-019-46979-y] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 07/09/2019] [Indexed: 11/25/2022] Open
Abstract
Although the understanding of excitation spectra in fluids is of great importance, it is still unclear how different methods of spectral analysis agree with each other and which of them is suitable in a wide range of parameters. Here, we show that the problem can be solved using a two-oscillator model to analyze total velocity current spectra, while other considered methods, including analysis of the spectral maxima and single mode analysis, yield rough results and become unsuitable at high temperatures and wavenumbers. To prove this, we perform molecular dynamics (MD) simulations and calculate excitation spectra in Lennard-Jones and inverse-power-law fluids at different temperatures, both in 3D and 2D cases. Then, we analyze relations between thermodynamic and dynamic features of fluids at (Frenkel) crossover from a liquid- to gas-like state and find that they agree with each other in the 3D case and strongly disagree in 2D systems due to enhanced anharmonicity effects. The results provide a significant advance in methods for detail analysis of collective fluid dynamics spanning fields from soft condensed matter to strongly coupled plasmas.
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Affiliation(s)
- Nikita P Kryuchkov
- Bauman Moscow State Technical University, 2nd Baumanskaya street 5, Moscow, 105005, Russia
| | - Lukiya A Mistryukova
- Bauman Moscow State Technical University, 2nd Baumanskaya street 5, Moscow, 105005, Russia
| | - Vadim V Brazhkin
- Institute for High Pressure Physics RAS, Kaluzhskoe shosse, 14, Troitsk, Moscow, 108840, Russia
| | - Stanislav O Yurchenko
- Bauman Moscow State Technical University, 2nd Baumanskaya street 5, Moscow, 105005, Russia.
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