Radiolysis of water ice in the outer solar system: Sputtering and trapping of radiation products

Abstract

Abstract. We performed quantitative laboratory radiolysis experiments on cubic water ice between 40 and 120 K, with 200 keV protons. We measured sputtering of atoms and molecules and the trapping of radiolytic molecular species. The experiments were done at fluences corresponding to exposure of the surface of the Jovian icy satellites to their radiation environment up to thousands of years. During irradiation, 02 molecules are ejected from the ice at a rate that grows roughly exponentially with temperature; this behavior is the main reason for the temperature dependence of the total sputtering yield. 02 trapped in the ice is thermally released from the ice upon warming; the desorbed flux starts at the irradiation temperature and increases strongly above 120 K. Several peaks in the desorption spectrum, which depend on irradiation temperature, point to a complex distribution of trapping sites in the ice matrix. The yield of 02 produced by the 200 keV protons and trapped in the ice is more than 2 orders of magnitude smaller than used in recent models of Ganymede. We also found small amounts of trapped H20 2 that desorb readily above 160 K.

The Production of Oxidants in Europa's Surface

“…Direct excitation of matrix-isolated H 2 O 2 at low temperature also did not yield O 2 , but the production of a mobile O that reacted with (Khriachtchev et al, 2000). Irradiating with 200 keV protons at temperatures of 40-129K, Bahr et al (2001) found only about 0.001-0.02% H 2 O 2 using programmed thermal desorption as compared with earlier experiments that suggested larger values (e.g., Table 2). Using infrared absorption Moore and Hudson (2000) found a G value of ,0.1 for incident MeV protons at low temperature, but the signal in the observed band became negligible at 80K, suggesting that H 2 O 2 was not being formed.…”

A mechanism for the production of hydrogen peroxide and the hydroperoxyl radical on icy satellites by low-energy electrons

“…The onset of this current indicates the vacuum level energy within an uncertainty of ±0.3 eV (Sanche, 1979). After electron bombardment, the D 2 O 2 and DO 2 yields were measured with the QMS by evaporating the film by resistive heating of the Pt foil (Bahr et al, 2001).…”

Formation of Hydrogen, Oxygen, and Hydrogen Peroxide in Electron‐irradiated Crystalline Water Ice

“…They found that the produced H 2 O 2 /H 2 O ratio is greater for the heavier ions ($6% for the case of Ar ++ ; only $1% for H + ). Bahr et al (2001) conducted quantitative laboratory radiolysis experiments on cubic water ice between 40 and 120 K with 200 keV protons. They found that trapped O 2 and H 2 O 2 can be released from the irradiated ice upon warming.…”