Intramolecular water-splitting reaction in single collisions of water ions with surfaces

Abstract

Direct water splitting into molecular hydrogen and atomic oxygen is demonstrated through single collisions of water ions with generic surfaces at hyperthermal energies.

Surface Science Investigations of Icy Mantle Growth on Interstellar Dust Grains in Cooling Environments

“…To date, the vast majority of electron/ion irradiation experiments on interstellar ice analogues focus on the chemistry induced upon exposure to ionizing bombardment; [131][132][133][134][135][136] fewer look at the desorbing species. [137][138][139][140] It is even rarer to see both processes compared, as in the work of Abdulgalil et al 141 This study reports that ion/electron induced chemistry is dominant in those environments where the ices are relatively thick (hundreds of layers thick), while EPD is significant when ices are thinner, which is the case as diffuse clouds transition to being dense clouds when reactive accretion has not yet reached a steady state. Consistency with what is known of the radiolysis of liquids and vapours 145,146 would suggest that H/H 2 production is likely to be an important process in photolysis and radiolysis of both simple (e.g.…”

Dynamic molecular oxygen production in cometary comae

“…However, neither H 2 O + nor D 2 O + ions, scattering on clean Pt, produce any discernible O 2 − signal. This is likely due to molecular hydrogen, present in the ultrahigh vacuum background or formed in situ by an intramolecular water-splitting reaction 18 , which scavenges O atoms from the Pt surface. The O-atom surface coverage must therefore be increased to overcome this problem, which is achieved readily by dosing the surface in situ with O 2 gas.…”

“…The formation of fast 16 O 16 O − may appear curious at first, as it requires the presence of 16 O on the surface. But it is readily accounted for by CID of H 2 16 O + ions 18 , which introduce 16 O or 16 OH to the Pt surface. As discussed above, H 2 16 O + bombardment produces no 16 O 16 O − signal unless the Pt surface is dosed with molecular oxygen.…”

“…Minerals found on the comet, such as olivine and pyroxene silicates 15 16 and Fe/Ni oxides 17 , are oxidized offering another potential source of oxygen. Thus, collisions of energetic water ions with oxidized minerals on the nucleus surface are probable, with several possible outcomes: (1) collision-induced dissociation (CID) of H 2 O + produces atomic O, atomic H and OH radicals and ions; (2) physical sputtering ejects mineral constituents, including metal and oxygen atoms; and (3) collisional excitation of H 2 O + drives an intramolecular water-splitting reaction 18 , producing molecular H 2 directly. But there is also a surprising forth outcome.…”

Detection of Negative Pickup Ions at Saturn's Moon Dione

“…It may therefore be possible that some surface‐mediated process, such as dissociative attachment to adsorbed O 2 or CO 2 as suggested by Teolis and Waite (2016), is implicated in the formation of the observed negative ions. Eley‐Rideal reactions between incident ions and surface material (Yao & Giapis, 2017a, 2017b) represent another possible negative ion formation pathway that may be relevant to icy moons and that deserves further study. However, we note that the scale height of the Dione exosphere is expected to be quite small, on the order of ~100 km (Sittler et al, 2004), and we cannot, given the accuracy of the CAPS observations, distinguish between negative pickup ions originating from the surface itself and those from the exosphere near the surface.…”