Hydrate sulfuric acid after sulfur implantation in water ice

Abstract

For many years an ongoing research program performed at our laboratory has had the aim to investigate the implantation of reactive ions in ices relevant to planetology by using IR spectroscopy. We present new results obtained by implanting 200 keV sulfur ions into water ice at 80K. We have looked at the formation of sulfur-bearing molecules such as sulfuric acid, sulfur dioxide and hydrogen sulfide. We find that hydrated sulfuric acid is formed with high yield (0.65 ± 0.1 molecules/ion). An upper limit to the production yield of SO 2 (Y≤ 0.025 molelcules/ion) has been estimated; no hydrogen sulfide has been detected. The formation of hydrogen peroxide is confirmed. Ozone is not detected. The results are discussed relevant to the inquiry on the radiolytic sulfur cycle considered responsible for the formation of sulfur-bearing molecules on the surfaces of the Galilean satellites. We demonstrate that sulfur implantation efficiently forms hydrated sulfuric acid whose observed abundance is explained as caused by an exogenic process. It is more difficult to say if the observed sulfur dioxide is quantitatively supported by only sulfur implantation; additional experimental studies are necessary along with direct observations, especially at UV wavelengths such as those that could be performed by instruments on board Hubble Space Telescope or by the forthcoming World Space Observatory (WSO/UV).

Molecular interactions with ice: Molecular embedding, adsorption, detection, and release

“…We looked at three inert projectiles: Xe, CF 4 , and SF 6 . Using TPD experiments, we showed that for Xe and CF 4 , the embedded gas that escapes at the lowest temperatures appears to be absorbed just below the surface.…”

“…For a comparison, we estimated the sizes from the van der Waals gas constants. 43 The radii are 2.73 Å for Xe, 2.93 Å for CF 4 , and 3.27 Å for SF 6 . This suggests that the size has some effect.…”

“…Another possibility is that it does penetrate, but it perturbs the ice enough that it is rapidly expelled from the selvedge. 6 is entrapped throughout the ice, some comes out as a "molecular volcano," with one narrow desorption peak at the position of the ASW to CI transition, where the near surface molecules can escape as cracks form in the ice. 41 The more deeply absorbed SF 6 then desorbs in concert with the D 2 O desorption.…”

“…These collisions deliver both energy and other species (C, S, N) leading to the chemical modification of the interior of the ice. [4][5][6][7] Energetic collisions of small molecules with ice surfaces are of particular relevance for the capture and matrix preconcentration of trace gases; 8,9 for gases with insufficient momentum are unable to penetrate into the ice, whereas heavier, or more energetic, species will be trapped in the near surface region of the solid. 10 Energetic collisions on ice surfaces are also highly relevant for the evolution of the composition of icy bodies in space.…”

“…Also, we wanted to more thoroughly explore the embedding rate as a function of projectile mass and energy. In this context, we also used two other relatively inert gases with very different masses, SF 6 and CF 4 . CF 4 has a strong IR signal, which allows for the use of time-resolved Fourier-transform reflection-absorption infrared spectroscopy (RAIRS) in addition to TPD.…”