Reactions of F⁺(³P) and F⁺(¹D) with silicon oxide. Possibility of spin-forbidden processes

High level ab initio and density functional theory calculations have been carried out to study the potential energy surfaces associated with the reactions of F⁺ in its ³P ground state and in its ¹D first excited state with silicon dioxide. The structures and vibrational frequencies of the stationary points of both potential energy surfaces were obtained at the B3LYP/6-31G(d) level. Final energies were calculated at the B3LYP/6-311+G-(3df,2p) and at the G3X levels of theory. [Si, O₂, F]⁺ singlet and triplet state cations present very different bonding characteristics. The most favorable reactions path in F⁺( ³P) + SiO₂ reactions Should yield O₂ + SiF ⁺, while in the reactions in the first excited state, only a charge exchange process, yielding F(2P) + SiO₂⁺-(²A), should be observed. However, both potential energy surfaces cross each other, because although the entrance F⁺(³P) + SiO₂ lies 34.5 kcal/mol below F⁺(¹D) + SiO₂, the global minimum of the singlet PES lies 10.3 kcal/mol below the global minimum of the triplet. The minimum energy crossing point between them is close to the global minimum, and the spin-orbit coupling is not zero, suggesting that very likely some of the products will be formed in the singlet hypersurface. The existence of instabilities and large spin-contamination in the description of some of the systems render the DFT calculations unreliable.