Reactions of F⁺(³P) and F⁺(¹D) with Silicon Oxide. Possibility of Spin-Forbidden Processes

Abstract

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 (3)P ground state and in its (1)D 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, O(2), F](+) singlet and triplet state cations present very different bonding characteristics. The most favorable reactions path in F(+)((3)P) + SiO(2) reactions should yield O(2) + SiF(+), while in the reactions in the first excited state, only a charge exchange process, yielding F((2)P) + SiO(2)(+)((2)A), should be observed. However, both potential energy surfaces cross each other, because although the entrance F(+)((3)P) + SiO(2) lies 34.5 kcal/mol below F(+)((1)D) + SiO(2), 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.