Refinement of Peterson and Levy's Neutron Diffraction Data on KHF2

The neutron-diffraction data obtained by Peterson and Levy from a single crystal of KHF2 have been refined in an attempt to settle the question of the geometry of the bifluoride ion in KHF2. It turns out to be impossible from the neutron diffraction data alone to distinguish a linear symmetric F–H–F ion from a linear one in which the hydrogen occupies two equally probable positions on either side of the center, even when these positions are 0.16 Å from the center. However, the agreement between the differences in mean-square amplitudes of vibration of hydrogen and fluorine along the bond as obtained from an analysis of the diffraction data and as calculated from spectroscopic data lends support to a linear symmetric model of the bifluoride ion in KHF2. The F–H–F distance is 2.277±0.006 Å.