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Crystallization in undercooled liquid microjets of H2/D2 mixtures

AutorFernández Sánchez, José María ; Kühnel, Matthias; Tejeda, Guzmán ; Moreno, Elena ; Kalinin, Anton; Grisenti, Robert E.; Montero, Salvador
Fecha de publicación2013
EditorUniversidad Pablo de Olavide
CitaciónIBER2013 XII Iberian Meeting on Atomic and Molecular Physics September 9-11, 2013 Universidad Pablo de Olavide (Sevilla, Spain)
ResumenNovel experiments on undercooled liquid microjets (filaments) of para-hydrogen (p-H2) and ortho-deuterium (o-D2) mixtures will be reported. These highly collimated filaments, less than 10 microns in diameter, are an ideal medium to produce undercooled liquid samples and to investigate the homogeneous solidification process, free from wall effects [1]. The filaments exit from cryogenic capillary nozzles into vacuum, to cool down fast by surface evaporation, with a temperature gradient across the jet due to their finite size radius and thermal conductivity. The filaments are monitored by laser shadowgraphy, and analyzed by means of high performance Raman spectroscopy [2], revealing their structure and temperature. The high spatial resolution of Raman spectroscopy allows observing in situ the structural changes of the liquid microjets, with a time resolution of ~10 ns. The filaments of pure p-H2 can be cooled down to 9 K (normal melting point at 13.8 K), before eventually solidifying at a crystal growth rate of ~33 cm/s [3]. Crystal growth rate in o-D2 is ~¿2 smaller, consistent with a collision-limited process [4]. Our experiments on diluted mixtures of o-D2 in p-H2 also show a dramatic slowing down in the crystallization kinetics of the mixture. Full path-integral Monte Carlo simulations show that the observed effect is a result of the (weak) zero-point contribution to the interaction potential between the particles. This favours the development in the undercooled liquid mixture of icosahedral local structures around the o-D2 solute molecules, and thus frustrates the p-H2 crystal growth. While our work strongly supports the view of an intrinsic link between local order and frustrated crystallization, it provides as well the first experimental evidence for the role played by quantum fluctuations during structural transformations in undercooled liquids. [1] R. E. Grisenti, R. A. Costa-Fraga, N. Petridis, R. Dorner, and J. Deppe, EuroPhys. Lett. 73, 540-546 (2006). [2] S. Montero, J. H. Morilla, G. Tejeda, and J. M. Fernandez, Eur. Phys. J. D 52, 31-34 (2009). [3] M. Kühnel, J. M. Fernández, G. Tejeda, A. Kalinin, S. Montero, and R. E. Grisenti, Phys. Rev. Lett. 106, 245301 (2011). [4] J. M. Fernández, M. Kühnel, G. Tejeda, A. Kalinin, R. E. Grisenti, and S. Montero, AIP Conf. Proc. 1501, 1296-1304 (2012).
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