Synergistic radiation effect on methyl silicone rubber of protons and electrons was investigated using a ground-based simulator for space radiation environment. The energy of protons and electrons was chosen as 150 keV, and the fluence 10¹⁶ cm^-2. The gas product is CH₃Si(O)CH₃ by mass spectrum after synthesized radiation. The quantum chemistry calculation indicated that the macro-molecule chains in the silicone rubbers could be fractured by a direct attack of H⁺ to the oxygen in the chains. This process was an only exothermic channel, giving out the heat of 655.34 kJ/mol. No stable transition states and intermediate products were formed, except for the fractured pieces of the chains. The calculation result was in agreement with the gas product CH₃Si(O)CH₃ formed by synergistic radiation of proton and electrons.

Key words: methyl silicone rubber, synergistic radiation of proton and electron, mass spectrum, quantum chemistry calculation, model for destruction