Radiolysis of Thin Water Ice in Electron Microscopy

Littleis known about the radiolysis of water ice, especially ascompared to the radiolysis of liquid water. In this study, the radiolyticdecomposition of thin water ice films is probed for an initial 80keV electron beam using electron energy loss spectroscopy, EELS. Pre-peaksin the oxygen K-edge spectra give the relative intensities of mostof the oxygen containing species produced by radiolytic water decomposition.Contrary to expectations from the extrapolation of liquid water radiolysisdata to high dose rates where significant H2O2 production is expected, the main molecular product observed in theoxygen K-edge EELS spectra of water ice is O-2. Significantmass loss of water and decomposition of most of its radiolytic productsare observed for higher exposures, and the O atom seems to have amajor role in the subsequent chemistry. An inverse relationship betweenthe formation of O-2 and of & BULL;OH is observed. A newhigh-dose reaction scheme is proposed. The significance of our resultswith respect to the radiolysis of water ice and for electron microscopystudies is discussed.