Refinement of Peterson and Levy's neutron diffraction data on KHF ₂

The neutron-diffraction data obtained by Peterson and Levy from a single crystal of KHFu 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 A 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 KHF ₂. The F-H-F distance is 2.277±0.006 Å.