Isotope exchange of D2O on H2O ice: Surface versus bulk reactivity

Abstract

The nature of the surface of crystalline water ice is investigated by monitoring isotope exchange in the first few bilayers. Near-monolayer amounts of D2O are deposited on thin films of H2O ice and isotope exchange at 145 K is monitored with Fourier-Transform infrared spectroscopy as a function of time. No exchange occurs on the surface of pure ice, however, exchange is readily observed on the surface of ice doped with small amounts of hydrogen chloride (HCl). The lack of exchange at the surface of pure ice stands in contrast to similar experiments performed of D2O embedded in the bulk. This suggests a depletion of mobile defects on the surface of pure crystalline ice at 145 K. This relative depletion may cause a significant difference between reactivity on the ice surface and in the ice bulk for other systems.

Proton mobility in thin ice films: a revisit

“…Park et al 11 adsorbed HCl onto an ice film and examined the H/D exchange reaction in surface water molecules. They observed that proton transfer was facile only in the lateral direction at the film surface, whereas vertical proton transfer to the film interior was almost absent at 90-140 K. The proton transport behaviors observed in these studies, i.e., mobile protons in ice [5][6][7][8][9] and vertically immobile protons at the ice surface, 10,11 seem to contradict each other. Recently, Lee et al 12,13 offered an explanation for this contradiction by showing that protons exhibit asymmetric transport behavior at the surface and interior of ice due to the thermodynamic affinity of protons for the ice surface.…”

“…Proton transport in ice is an important process related to electrical conductivity 1,2 and chemical reactivity of ice, 3 and this subject has been studied by numerous researchers for a long time. [1][2][3][4][5][6][7][8][9][10][11][12][13] The experimental results on the mobility of protons in ice, however, vary widely; whereas some studies claim that proton mobility in ice crystals is faster than that in liquid water, 4 other studies indicate that proton transport is a thermally activated process that occurs substantially slowly in ice at low temperature [5][6][7][8][9] or even not at all. 10 Devlin and coworkers [5][6][7] studied the H/D isotopic exchange in water molecules in ice nanocrystals at a temperature below 145 K using IR spectroscopy, and suggested that the H/D exchange occurred via proton transfer between water molecules and subsequent movement of Bjerrum defects (the ''hop-and-turn'' mechanism).…”

Isotope Effect of Proton/Deuteron Diffusion Constant in Ice

“…We found that the proton diffusion in ice I h at 240–263 K is about 10 times larger than in liquid water at 295 K. Ice is a poor solvent, and as a consequence, the photoacid molecules are expelled from the bulk and tend to aggregate at the grain boundaries. The experimental results on the mobility of protons in thin‐film ice indicate that proton transport is a thermally activated process that occurs rather slowly in ice at low temperature 22–28 or even not at all 29 . In previous work, 21,30,31 to overcome the tendency of the photoacid to aggregate at the grain boundaries, we added a small mole fraction (0.1–1%) of methanol to the aqueous solution.…”

Dynamics and unsteady morphologies at ice interfaces driven by D 2 O–H 2 O exchange

“…The fractionation of water isotopomers is a manifestation of preferential freezing of D 2 O with respect to H 2 O, which affects the distribution of environmental deuterium (11,12). Isotopic fractionation also can occur through H/D exchange, a process that has been investigated at temperatures ranging from −178 • C to −2 • C (13)(14)(15)(16)(17)(18)(19)(20). H/D exchange at lower temperatures (up to −103 • C) has been investigated by measurement of changes in isotopic composition in thin stratified films of D 2 O-H 2 O-HDO (1-100 nm in thickness) (13,14,17,19).…”

“…Isotopic fractionation also can occur through H/D exchange, a process that has been investigated at temperatures ranging from −178 • C to −2 • C (13)(14)(15)(16)(17)(18)(19)(20). H/D exchange at lower temperatures (up to −103 • C) has been investigated by measurement of changes in isotopic composition in thin stratified films of D 2 O-H 2 O-HDO (1-100 nm in thickness) (13,14,17,19). The diffusion of tritium into bulk H 2 O ice has been measured over the range −35 • C to −2 • C (18,20), with diffusion coefficients spanning seven orders of magnitude.…”