title: Raman Measurements of Pure Hydrogen Clathrate Formation from a Supercooled Hydrogen-Water Solution.
abstract: The nucleation and growth of a solid clathrate hydrate from the liquid phase is a process that is even less understood and more difficult to study than the nucleation of a solid phase from a pure liquid. We have employed in situ Raman spectroscopy to study the hydrogen-water supercooled solution undergoing clathrate formation at a pressure of about 2 kbar and temperature of 263 K. Raman light scattering detects unambiguously the H2 molecules inside of clathrate crystallites, which change stoichiometry during growth. The spectral intensity of the hydrogen vibrational band shows the time evolution of the population of the large and small cages, demonstrating that, in the initial stages of clathrate formation, the occupation of the large cages is quite lower than its equilibrium value. From the measurement of the growth rate of the crystallites, we demonstrate that the growth of the clathrate in the liquid is a diffusion-limited process.
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi , via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy.|Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze , via Sansone 1, I-50019 Sesto Fiorentino, Italy.
authors.forename: Leonardo
authors.initials: L
authors.lastname: del Rosso
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi , via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy.
authors.forename: Milva
authors.initials: M
authors.lastname: Celli
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi , via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Ulivi
keywords: Raman spectroscopy; crystal growth; high pressure; hydrogen clathrates; nucleation