Time-Resolved Study of Crystallization in Deeply Cooled Liquid Parahydrogen

We present real-time measurements of the crystallization process occurring in liquid para-hydrogen (para-H-2) quenched to approximate to 0.65T(m) (T-m 13.8 K is the melting point of bulk liquid para-H-2). The combination of high spatial resolution Raman spectroscopy and liquid microjet generation allows, in situ, capturing structural changes with similar to 10(-8) s time resolution. Our results provide a crystal growth rate that rules out a thermally activated freezing process and reveal that the quenched melt freezes into a metastable polymorph, which undergoes a structural transition. The achieved temporal control offers new opportunities for exploring the elementary processes of nonequilibrium phase transformations in supercooled liquids.