The radio frequency and microwave spectrum of KrClF has been measured by molecular beam electric resonance spectroscopy. The molecular constants for the major isotope (84Kr35ClF) are:[Formula: see text]The atomic arrangement is Kr—Cl—F with a linear equilibrium structure and the vibrationally averaged 84Kr—35Cl distance is 3.3884 Å. The molecular structure is very similar to that of ArClF, previously studied in this laboratory. Vibrational frequencies, force constants, estimated well depths, dipole moments, and distances in the two molecules are compared. Molecular constants of the four KrClF isotopes studied are used to derive a vibrational force field for the molecule, including anharmonic and bend–stretch coupling terms. A brief summary of the four linear van der Waals molecules studied spectroscopically in this laboratory is presented, along with a simple and structurally predictive model of the van der Waals bond.
