Ab initio SCF and MRD CI studies of the FHCl− ion

The equilibrium geometry and hydrogen-bonding energy of the heterobihalide ion FHCl^? have been calculated by ab initio SCF and MRD CI methods using an AO basis set of near Hartree-Fock quality. In the most stable (linear) conformation of this ion, the equilibrium F Cl/FH distances are predicted to be 5.657/1.754, 5.453/L800 and 5.437/1.801 bohr by SCF, MRD CI and full CI (estimated) calculations respectively. A second minimum, which is of extremely small depth and corresponds to the hydrogen atom near the chlorine atom, begins to appear in the potential surface at an FCl distance of about 6.0 bohr. The hydrogen-bonding energy of FHCl^? lies in the range 18–22 kcal/mol.