Barrier Height for the Exchange Reaction F + HF → FH + F

There exists a body of conflicting data as to the existence or nonexistence of FHF, ClHCl, BrHBr, and IHI as chemically bound molecular species. Ab initio quantum mechanical electronic structure calculations are presented which predict linear symmetric FHF to be unstable. The barrier height for the F + HF exchange reaction is suggested to be no less than 18 kcal/mol, much larger than expected either intuitively or on the basis of certain experiments on related systems. The expected reliability of the calculations is based upon comparable results for diatomic molecules and the F + H2and H + F2potential energy surfaces.