title: Crystallization kinetics and excess free energy of H2O and D2O nanoscale films of amorphous solid water.
abstract: Temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) are used to investigate the crystallization kinetics and measure the excess free energy of metastable amorphous solid water films (ASW) of H(2)O and D(2)O grown using molecular beams. The desorption rates from the amorphous and crystalline phases of ASW are distinct, and as such, crystallization manifests can be observed in the TPD spectrum. The crystallization kinetics were studied by varying the TPD heating rate from 0.001 to 3 K/s. A coupled desorption-crystallization kinetic model accurately simulates the desorption spectra and accurately predicts the observed temperature shifts in the crystallization. Isothermal crystallization studies using RAIRS are in agreement with the TPD results. Furthermore, highly sensitive measurements of the desorption rates were used to determine the excess free energy of ASW near 150 K. The excess entropy obtained from these data is consistent with there being a thermodynamic continuity between ASW and supercooled liquid water.
authors.affiliation: Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, P.O. Box 999, Mail Stop K8-88, Richland, Washington 99352, USA. Scott.Smith@PNL.gov
authors.forename: R Scott
authors.initials: RS
authors.lastname: Smith
authors.forename: Jesper
authors.initials: J
authors.lastname: Matthiesen
authors.forename: Jake
authors.initials: J
authors.lastname: Knox
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Kay
mesh_terms: D003460:Crystallization; D017666:Deuterium Oxide / Q000737:chemistry*; D007700:Kinetics; D008567:Membranes, Artificial; D049329:Nanostructures / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D008567:Membranes, Artificial; D014867:Water; D017666:Deuterium Oxide