An electron diffraction study of alkali fluoride vapors

The structures of NaF, KF, RbF, and CsF in the vapor phase were determined via standard electron diffraction counting techniques with nozzle temperatures ranging from 798 to 1123 K. The reactivity of the fluorides combined with the higher temperature requirements necessitated a new nozzle design as well as modification to the oven. The data analysis yielded the structure parameters and the ratio of monomeric to dimeric compounds. The mean amplitudes of vibration of the monomeric molecules were held at values based on microwave frequencies and the harmonic potential approximation. The corrected monomer distances re agree well with microwave-spectroscopy results. Rhombic geometries with bonded dimer distances ranging from 2.08 to 2.70 Å were observed. The F–M–F bond angles were found to be nearly constant, varying only from 82.2° to 85.5°. The dimer mole fractions in the vapor were observed to vary from 5% to 18%. There were no significant amounts of any trimeric species observed in the vapor. The observed dimer mole fractions were compared with existing measurements from velocity selection experiments and found to be in excellent agreement. The dimer mole fractions were also compared with various theoretical predictions.