Theoretical study of reactive processes in the FH+2 system by a b i n i t i o MCSCF–CI and diatomics-in-molecules calculations

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Abstract
Ab initio MCSCF–CI calculations of the diatomic potential curves of HF+ arising from H++F(2P) and F+(3P)+H(2S) atoms are used in the diatomics‐in‐molecules (DIM) formalism to obtain potential energy surfaces for six 3A′ and six 3A″ states of FH+2. Energy splittings between the two lowest 3A′ surfaces in the region of an ’’avoided crossing’’ seam in the entrance channel are made to agree with ab initio calculations on the triatomic FH+2. The resulting DIM surfaces are used to find energetically accessible pathways for the reaction F+(3P)+H2(X 1Σ+g) →HF+(X 2Π)+H and related reactions which have been observed experimentally. Empirical approximations to the interaction between F+(1D) and H atoms are used in constructing model diabatic potential surfaces for the 1A′ states of FH+2. Intersections of these surfaces illustrate what products might be expected from the reaction of F+(1D) metastable ions with H2 molecules; our results support recent experimental evidence that the dynamics of F+(1D) ions reacting with H2 are quite different from those of F+(3P) ions.