## Abstract

Ab initio calculations have been performed on the linear symmetric configuration of KrF2, using a 993-configuration “first-order” wave function and an extended basis set of Slater functions. These calculations yield a bound potential curve with respect to three infinitely separated atoms; the Kr–F bond distance is 1.907 Å and the dissociation energy is 0.39 eV, as compared to the experimental values of 1.889 ± 0.01 Å and 1.013 eV, respectively. A potential maximum is found at Kr–F distance 2.42 Å, lying 0.22 eV above the dissociation limit. The electric field gradient at the Kr nucleus, near the potential minimum, is very near the self-consistent field (SCF) value for an isolated Kr+ ion but drops rapidly to zero near the potential maximum. These results show that the Kr–F bond is ionic in nature near the equilibrium separation and becomes covalent at larger separations, as proposed by Coulson. In contrast to the “first-order” wave function results, one configuration SCF calculations yield an attractive potential curve with a minimum at 1.813 Å and 2.98 eV above the SCF energy of three separated atoms. This behavior is permitted because the one-configuration SCF wave function does not dissociate to neutral separated atoms. However, two-configuration SCF calculations which allow proper dissociation to neutral separated atoms yield a repulsive potential curve with an inflection point near 1.85 Å. Cl calculations using the two-configuration SCF occupied orbitals and including all eight valence shell configurations yield results quantitatively similar to the two-configuration SCF results. In addition, a series of SCF calculations has been carried out to study the importance of polarization functions. The results indicate that 4d functions centered on Kr are much less important than suggested by minimum basis set calculations. Finally, Koopmans' theorem ionization potentials are compared with the experimental photoelectron spectrum. © 1972, American Chemical Society. All rights reserved.