Photoelectric emission from the alkali metal doped vacuum-ice interface

Abstract

The photoelectron photoemission spectra and thresholds for low coverages of Li and K adsorbed on water-ice have been measured, compared with photoionization spectra of the gas-phase atoms, and modeled by quantum chemical calculations. For both alkali metals the threshold for photoemission is dramatically decreased and the cross section increased on adsorption to the water-ice surface. Quantum chemical calculations suggest that the initial state is formed by the metal atoms adsorbed into the water-ice surface, forming a state with a delocalized electron distribution. This state is metastable and decays on the hundreds of seconds time scale at 92 K. The decay is markedly faster for Li than for K, probably due to diffusion into the ice film.

The fate of meteoric metals in ice particles: Effects of sublimation and energetic particle bombardment

“…Once KOH has formed, the dangling H atom can easily migrate across the surface to find another dangling H and form H 2 . The energy involved in converting the adsorbed K to KOH is consistent with the decay rate of K of 5 × 10 -3 s -1 on ice at 92 K (Vondrak et al, 2009).…”

“…Both the primary and secondary peaks of K and KOH occur at similar distances into the ice, suggesting KOH is formed wherever K is present. In the previous photoelectric emission study, the K signal on the ice decayed with an e-folding time of 200 s at 92 Vondrak et al, 2009). Given that the ice temperature in the present study was 110 K and the reaction rate is likely to have a positive temperature dependence by analogy with Na (Vondrak et al, 2006), and that there was a 60 minute delay between deposition of the K and sputtering in our experiments, it is very likely that complete conversion of K to KOH in the ice layer was occurring.…”

“…Photoelectric emission from K, Na and Li deposited at low coverage on an ice surface has also been studied (Vondrak et al, 2006;Vondrak et al, 2009). The presence of these alkali metal atoms on the ice surface substantially reduces the photoelectric work function; however, the effect is short-lived (hundreds of seconds time scale at 92 K), presumably because the metals react in the ice to form hydroxides.…”

Ultrafast Dynamics at the Na/D2O/Cu(111) Interface: Electron Solvation in Ice Layers and Na+-Mediated Surface Solvation

“…The interaction of Na atoms with amorphous water ice has already been studied before experimentally and theoretically. ,,− These previous investigations show that, after deposition of neutral Na atoms on the ice surface, the 3s electron of the Na is spontaneously liberated into the water environment, resulting in the formation of Na + ions. For elevated temperatures (>110 K) and Na concentration above 0.2 ML, this electron transfer results in the exothermic dissociation of surroundings water molecules to form OH − ions and leads to the formation of NaOH.…”