Proton segregation on a growing ice interface

Lilach, Yigal; Iedema, Martin J.; Cowin, James P.

doi:10.1016/j.susc.2008.07.008

Cited by 16 publications

(29 citation statements)

References 18 publications

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“…It is interesting that the segregative behavior at ice surfaces appears for hydroxide ions as well as hydronium ions. [4][5][6][7][8][9] Two types of transport mechanisms were identified for hydroxide ions in ice. At 90 K, a small portion of hydroxide ions are transported from the ice film interior to the surface by a proton hopping mechanism, which is conceptually a mirror image of the transport mechanism of hydronium species in ice.…”

Section: Discussionmentioning

confidence: 99%

“…Previous studies [4][5][6][7][8][9] have shown that hydronium ions, like hydroxide ions, have a thermodynamic affinity for the ice surface. The surface preference displayed by both hydronium and hydroxide ions, although they are oppositely charged, raises an interesting question of chemical origin.…”

Section: A Surface Preference Of Hydroxide Ionsmentioning

confidence: 99%

“…2,3 Recent studies have shown that protons tend to reside at the surface of ice films rather than in the interior. [4][5][6][7][8][9] Surface accumulation of protons can facilitate acid-base reactions with basic adsorbates on the surface. [10][11][12][13][14][15] The transport mechanisms of protons within ice or on its surface have been investigated in detail using various spectroscopic tools, including FTIR, [16][17][18] NMR, 19 low energy sputtering (LES) and Cs + reactive ion scattering (RIS), 4,5,20 and time-resolved fluorescence emission measurements.…”

Section: Introductionmentioning

confidence: 99%

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Segregation of hydroxide ions to an ice surface

Kim

Park

Kang

2011

The Journal of Chemical Physics

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Hydroxide ions that are initially buried within an ice film segregate to the ice film surface at elevated temperatures. This process was observed by conducting experiments with an ice film constructed with a bottom H(2)O layer and an upper D(2)O layer, with an excess of hydroxide ions trapped at the H(2)O/D(2)O interface as they were generated by Na hydrolysis. The transport of hydroxide ions from the interfacial layer to the surface was examined as a function of time using a low energy sputtering method. The progress of the H/D exchange reaction in surface water molecules was also monitored with the Cs(+) reactive ion scattering technique. At 90 K, only a small portion of buried hydroxide ions moved to the surface in the form of OD(-) species. This was due to hydroxide transport via proton hopping through a D(2)O layer, 3 BL thick, in the surface region. At 135 K, at which point water self-diffusion is active in the ice film, the majority of the buried hydroxide ions segregated to the surface after ∼1 h. Both OH(-) and OD(-) species were produced at the surface, at an OH(-)/OD(-) population ratio ≥1. Based on kinetic measurements for the transport of OH(-) and OD(-) species and the H/D exchange of surface water molecules, we concluded that the major transport channel for hydroxide ions in this regime is the migration of molecular hydroxide species. H/D exchange reactions also occur between surface hydroxide ions and water molecules. No evidence was observed for the occurrence of the hop-and-turn process at 135 K, although it is known as an important mechanism of proton transport in ice.

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Section: Discussionmentioning

confidence: 99%

Section: A Surface Preference Of Hydroxide Ionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Segregation of hydroxide ions to an ice surface

Kim

Park

Kang

2011

The Journal of Chemical Physics

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“…Most recently, there have been reports of elegant isotopic exchange experiments (11), which show that ice surfaces have a significant role in controlling the concentration of ionic and Bjerrum defects and suggest that hydronium ions are surface segregated (12)(13)(14). A further consideration is the disordered proton structure of ice Ih.…”

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confidence: 99%

Point defects at the ice (0001) surface

Watkins

VandeVondele²,

Slater³

2010

Proc. Natl. Acad. Sci. U.S.A.

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Using density functional theory we investigate whether intrinsic defects in ice surface segregate. We predict that hydronium, hydroxide, and the Bjerrum L-and D-defects are all more stable at the surface. However, the energetic cost to create a D-defect at the surface and migrate it into the bulk crystal is smaller than its bulk formation energy. Absolute and relative segregation energies are sensitive to the surface structure of ice, especially the spatial distribution of protons associated with dangling hydrogen bonds. It is found that the basal plane surface of hexagonal ice increases the bulk concentration of Bjerrum defects, strongly favoring D-defects over L-defects. Dangling protons associated with undercoordinated water molecules are preferentially injected into the crystal bulk as Bjerrum D-defects, leading to a surface dipole that attracts hydronium ions. Aside from the disparity in segregation energies for the Bjerrum defects, we find the interactions between defect species to be very finely balanced; surface segregation energies for hydronium and hydroxide species and trapping energies of these ionic species with Bjerrum defects are equal within the accuracy of our calculations. The mobility of the ionic hydronium and hydroxide species is greatly reduced at the surface in comparison to the bulk due to surface sites with high trapping affinities. We suggest that, in pure ice samples, the surface of ice will have an acidic character due to the presence of hydronium ions. This may be important in understanding the reactivity of ice particulates in the upper atmosphere and at the boundary layer.DFT | first-principles | water | interface T he surface of ice acts as a catalyst in the upper atmosphere yielding halogen containing species that facilitate the destruction of ozone (1). More generally, probing the structure/activity relationship of ice with trace gases is important, topical, and yet difficult in the laboratory. Here, we use computational approaches to address the fundamental question of whether charged defects in ice show a tendency to locate at the surface in preference to the crystal interior.

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“…Apart from these works investigating the effects of photon radiation on ice, the properties of H 3 O + in ice have been extensively studied using ice samples doped with strong acids or acid precursors. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] These investigations have greatly improved our understanding about the mobility of H 3 O + in ice, the transport mechanisms, [24][25][26][27][28][29][30][31][32][33][34][35] and the reactivity toward base molecules. [36][37][38] In an earlier communication, 22 we reported the occurrence of the protonation of methylamine (MA; CH 3 NH 2 ) adsorbates on an ice film exposed to UV radiation, which indicated the formation of H 3 O + in the ice.…”

Section: Introductionmentioning

confidence: 99%

Metastable hydronium ions in UV-irradiated ice

Moon

Kang

2012

The Journal of Chemical Physics

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We show that the irradiation of UV light (10-11 eV) onto an ice film produces metastable hydronium (H(3)O(+)) ions in the ice at low temperatures (53-140 K). Evidence of the presence of metastable hydronium ions was obtained by experiments involving adsorption of methylamine onto UV-irradiated ice films and hydrogen-deuterium (H∕D) isotopic exchange reaction. The methylamine adsorption experiments showed that photogenerated H(3)O(+) species transferred a proton to the methylamine arriving at the ice surface, thus producing the methyl ammonium ion, which was detected by low energy sputtering method. The H(3)O(+) species induced the H∕D exchange of water, which was monitored through the detection of water isotopomers on the surface by using the Cs(+) reactive ion scattering method. Thermal and temporal stabilities of H(3)O(+) and its proton migration activity were examined. The lifetime of the hydronium ions in the amorphized ice was greater than 1 h at ∼53 K and decreased to ∼5 min at 140 K. Interestingly, a small portion of hydronium ions survived for an extraordinarily long time in the ice, even at 140 K. The average migration distance of protons released from H(3)O(+) in the ice was estimated to be about two water molecules at ∼54 K and about six molecules at 100 K. These results indicate that UV-generated hydronium ions can be efficiently stabilized in low-temperature ice. Such metastable hydronium ions may play a significant role in the acid-base chemistry of ice particles in interstellar clouds.

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Proton segregation on a growing ice interface

Cited by 16 publications

References 18 publications

Segregation of hydroxide ions to an ice surface

Segregation of hydroxide ions to an ice surface

Point defects at the ice (0001) surface

Metastable hydronium ions in UV-irradiated ice

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