FTIR Studies of Annealing Processes in Low Temperature Pure and Mixed Amorphous Ice Samples

Abstract

Thin ice films produced by vapor deposition upon a bare CsI window as well as upon predeposited rare-gas layers or by co-deposition with rare gases may bear similarities to ices in the stratosphere and interstellar space. It was found that infrared band peak positions, bandwidths, and integrated intensities, especially those of the coupled and decoupled OH stretching mode bands, are very sensitive to structural modifications in the solid ice layers. Abrupt changes in the temperature-dependent curves of these parameters signify processes such as annealing, morphological changes, phase transitions, release of internal gas inclusions and of externally adsorbed gases, and ice grain ejection. It was shown that (H 2 O) as annealing is a gradual process taking place even at very low temperatures. Spectroscopic similarities exist between the bulk porous ice formed by rare gas release and supercooled water solid and both differ significantly in their infrared spectra from the usual vapor-deposited amorphous ices.

Density and index of refraction of water ice films vapor deposited at low temperatures

“…Under similar growth conditions Drobyshev 12 obtained a temperature dependence of the index of refraction at 14 m that implies an ice density that decreases with decreasing temperature. In contrast, Givan et al, 38 who use monodirectional deposition from a single narrow nozzle, find that ice condensed onto CsI at 5 K does not have a measurable porosity. We propose that the direction of the gas flow has an important effect in film density and morphology.…”

“…Such low values at 20 K are consistent with those from other studies 20,25 but contrast with a recent report that ice grown at 5 K has no discernible porosity. 38 Below about 40 K, condensation of ice leads to an amorphous phase that has a high intrinsic density, i ϭ1.1 g/cm 3 . 36,39,40 In this work, we combined vacuum microbalance and optical interference techniques to determine directly the density and index of refraction of vapor-deposited ice.…”

Laboratory Simulation of Competition between Hydrogenation and Photolysis in the Chemical Evolution of H2O‐CO Ice Mixtures

“…The successive formation of H 2 CO and CH 3 OH was observed with the consumption of CO. In Figure 5b, the dip labeled A at 3660 cm À1 corresponds to the decrease of OÀH stretching band arising from the interaction of H 2 O and CO (Givan et al 1997). The absorbance of this band decreased due to the consumption of CO neighboring H 2 O.…”

VLT-ISAAC 3–5 μm spectroscopy of embedded young low-mass stars

“…As soon as the grain is warmed to 12-15 K by the luminosity of the object, CO molecules can diffuse into the ice and form new bonds, changing the morphology of the mixture and thus the profile at 4.67 µm, or they can sublime back to the gas phase (Al-Halabi et al 2004;Collings et al 2003;Givan et al 1997). The mobility of CO and its high abundance in cold icy mantles also explain why it is a key species for surface reactions leading to polyatomic molecules such as CO 2 and CH 3 OH (Rodgers & Charnley 2003;Chiar et al 1998;Teixeira et al 1998).…”