Electron-Induced Decomposition of Condensed Acetone Studied by Quantifying Desorption and Retention of Volatile Products

The electron-induced decomposition of thin condensed layers of acetone was studied by a combination of electron-stimulated desorption (ESD) experiments and thermal desorption spectrometry (TDS) monitoring both the decay of acetone and the formation of volatile products. A reaction mechanism for the decay is proposed and its validity verified by modeling the TDS and ESD data on the basis of a set of resulting elementary rate equations. The results show that ESD data as a function of electron exposure also give indirect evidence of the presence of nonvolatile species. In particular, formation and desorption of CO is delayed because part of the carbonyl groups become incorporated in larger nonvolatile compounds. These, in turn, decompose upon further electron exposure to release CO. ESD curves obtained below the desorption temperature of the small volatile products CO and CH4 have also been reproduced well assuming that acetone layers have a limited capacity for uptake of volatile species and become saturated with these products during decomposition. Finally, we show that the quantitative evaluation of ESD data obtained above and below the desorption temperature of small volatile products in principle offers an approach to a quantitative comparison of product amounts desorbing in ESD and postirradiation TDS.