CO2 and C2H4 grafting to the native defects of ion-bombarded porous silica

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)₄, though it is expected to relax via formation of peroxidic bridges), and the oxygen-bridge vacancy (which in the absence of relaxation can be described as a diradical center (≡Si^•)₂– the E^′′ center). These radicals react with the residual atmosphere according to completely new pathways: the bombardment in a CO₂ atmosphere results in the formation of ester-like and carboxylate groups, stable up to 500 °C at least, inserted in the SiO₂ network at the oxygen-bridge vacancies. The bombardment in a C₂H₄ atmosphere results in more complex configurations: the oxygen-bridge vacancy reacts at room temperature with ethylene forming a Lewis adduct which, after heating at 500 °C, presumably reverts to a -CH₂-CH₂- bridge in between silicon atoms; the silicon-link vacancy likely reacts with C₂H₄ forming CH₃CHO. These conclusions, based on experimental data (mainly infrared spectroscopy), are also supported by extended quantum mechanical calculations (density-functional methods and ab initio molecular dynamics).