REACTIONS OF SILICA STRAINED RINGS - AN EXPERIMENTAL AND AB-INITIO STUDY

Ab-initio techniques inclusive of electron correlation (accounted for through both the perturbative MP2 method and the local and gradient-corrected density functional methods) are used in conjunction with IR spectroscopy of surface species to study the reaction of a few molecules with the strained four-atom rings present at the surface of amorphous silica outgassed at high temperature, mimicked in the calculations by cyclodisiloxane. Slightly acidic molecules like water are known to react under mild conditions; attempts have been made to activate N-2, CO2, H-2 and H2CO in a microwave discharge. Only with H, reaction has been observed. In full agreement with the experiment, calculated standard free enthalpies of reaction and activation energies show that reaction is: (i) facile with water; (ii) possible though somewhat activated with hydrogen; (iii) thermodynamically not allowed with carbon dioxide; (iv) by no means possible with molecular nitrogen.