Interactions of CCl₄ with Thin D₂O Amorphous Ice Films. 2. Variation of Desorption Kinetics with Ice Preparation Conditions and Evidence for Distinct Structures of Low-Density Amorphous Ice

Abstract

High sensitivity temperature-programmed desorption mass spectrometry (TPDMS) was employed in order to investigate the desorption kinetics of CCl 4 from thin (∼500 ML (ML: monolayer)) amorphous D 2 O ice films. TPDMS experiments demonstrate that at low coverages CCl 4 is trapped in the pores near the surface of microscopically rough ice. Three distinct desorption features, µ-, δ-, and -CCl 4 , consistent with the release of trapped CCl 4 were observed. The µ-, δ-, and -CCl 4 desorption yields demonstrate high sensitivity to the temperature and rate of ice film deposition. We interpret these results as evidence of the existence of three metastable forms of microporous amorphous ice, I µ , I δ , and I . Measurements of the relative desorption yields from CCl 4 species trapped at the surface of ice films prepared at different temperatures and deposition rates were used in order to estimate the barriers to the diffusion of D 2 O on the surface of I δ (E Dδ ) and I (E D ). The values obtained were E Dδ ) 5 ( 1 kcal mol -1 and E D ) 9 ( 2 kcal mol -1 . We suggest that I µ , I δ , and I can be characterized respectively by the relative abundances of two-, three-, and four-coordinated D 2 O molecules at the ice surface. A proposed phase diagram for thin D 2 O ice films is presented.

Probing the interaction of amorphous solid water on a hydrophobic surface: dewetting and crystallization kinetics of ASW on carbon tetrachloride

“…12,17 The interaction of CCl 4 with ASW has been previously studied by us 32 and others. 36,37 When heated, ASW begins to crystallize. This crystallization induces cracking which opens a connected pathway between the underlayer and the external environment.…”

Dependence of the adsorption of halogenated methane derivatives at the ice surface on their chemical structure

“…Further, the majority of these studies were performed at considerably lower temperatures than what corresponds to tropospheric conditions (i.e., 200-220 K). Thus, the interaction of CCl 4 with the ice surface was studied by temperature programmed desorption (TPD) below 130 K [15][16][17]; the surface of ice nanocrystals was characterised using CF 4 as a surface probe at 83 K [18], and the adsorption of CF 4 on amorphous ice was investigated both by volumetric and Fourier transformation infrared spectroscopy (FTIR) measurements at 95 K [19]. All these studies led to the general conclusion that these tetrahedral molecules with the general formula of CX 4 (X being a halogen atom) are rather weakly bound to the ice surface, and their adsorption depends on surface coverage, as the adsorption layer grows according to a three-dimensional clustering mechanism.…”

Photodissociation of methyl iodide adsorbed on low-temperature amorphous ice surfaces

“…The feature at 120 K, shown in Figures 1(a) and 1(b), represents the desorption of CH 3 I monomers and weakly interacting islands. 46 According to previous studies of CCl 4 on PASW ice, 14 adsorbates fill pores before occupying terminal surface sites. Therefore, when CH 3 I was deposited on PASW, the pores were filled before CH 3 I began to accumulate on the surface.…”