molecules Article Optical Diagnostics of Supercritical CO2 and CO2-Ethanol Mixture in the Widom Delta Evgenii Mareev 1,2,* , Timur Semenov 2,3, Alexander Lazarev 4, Nikita Minaev 1 , Alexander Sviridov 1, Fedor Potemkin 2 and Vyacheslav Gordienko 1,2 1 Institute of Photon Technologies of Federal Scientific Research Centre “Crystallography and Photonics” of Russian Academy of Sciences, Pionerskaya 2, Troitsk, 108840 Moscow, Russia;
[email protected] (N.M.);
[email protected] (A.S.);
[email protected] (V.G.) 2 Faculty of Physics, M. V. Lomonosov Moscow State University, Leninskie Gory bld.1/2, 119991 Moscow, Russia;
[email protected] (T.S.);
[email protected] (F.P.) 3 Institute on Laser and Information Technologies—Branch of the Federal Scientific Research Centre “Crystallography and Photonics” of Russian Academy of Sciences, Svyatoozerskaya 1, Shatura, 140700 Moscow, Russia 4 Faculty of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory bld.1/2, 119991 Moscow, Russia;
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[email protected] Academic Editors: Mauro Banchero and Barbara Onida Received: 26 October 2020; Accepted: 17 November 2020; Published: 19 November 2020 Abstract: The supercritical CO2 (scCO2) is widely used as solvent and transport media in different technologies. The technological aspects of scCO2 fluid applications strongly depend on spatial–temporal fluctuations of its thermodynamic parameters. The region of these parameters’ maximal fluctuations on the p-T (pressure-temperature) diagram is called Widom delta. It has significant practical and fundamental interest. We offer an approach that combines optical measurements and molecular dynamics simulation in a wide range of pressures and temperatures.