Structural Evolution of Supercritical CO2 across the Frenkel Line.
Here, we study structural properties of the supercritical carbon dioxide and discover the existence of persistent medium-range order correlations, which make supercritical carbon dioxide nonuniform and heterogeneous on an intermediate length scale. We report on the CO2 heterogeneity shell structure where, in the first shell, both carbon and oxygen atoms experience gas-like-type interactions with short-range order correlations while within the second shell, oxygen atoms essentially exhibit a liquid-like type of interactions due to localization of transverse-like phonon packets. Importantly, we highlight a catalytic role of atoms inside of the nearest-neighbor heterogeneity shell in providing a mechanism for diffusion and proving the existence of an additional thermodynamic boundary in the supercritical carbon dioxide on an intermediate length scale. Finally, we discuss important implications for answering the intriguing question whether Venus may have had CO2 oceans and urge for an experimental detection of this persistent local-order heterogeneity.
†Baker Laboratory, Cornell University, Ithaca, New York 14853, United States.
Dima
D
Bolmatov
‡Volgograd State Technical University, Volgograd, 400005 Russia.
D
D
Zav'yalov
¶Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom.
M
M
Gao
§Brookhaven National Laboratory, Upton, New York 11973, United States.
Mikhail
M
Zhernenkov
Venus’s atmosphere; order within disorder; phonon localization; structural crossover; supercritical carbon dioxide