The normal coordinates of PF 5 are examined using the Coriolis zeta constants and mean vibrational amplitudes as additional constraints to the vibrational problem. The Coriolis coupling parameters, determined from gas-phase band contour measurements, satisfactorily limit the force constants for the E' symmetry species. An analysis of the potential energy distributions for the degenerate modes of PF 5 places the axial PF 2 bending deformation at a higher frequency than the in-plane PF 3 bending motion. A consideration of the E' modes for AsF 5 indicates an analogous assignment for the bending vibrations. In an attempt to limit the A' 1 and A″ 2 force constants for PF 5, the vibrational amplitudes were computed for a wide range of the F12 and F34 interaction force constants, while fixing the force field for the E' species from the zeta constant calculations. Comparisons between the experimental and calculated vibrational amplitudes indicate an insufficient sensitivity of these parameters to the potential function for limiting the interaction force constants as narrowly as the Coriolis data. The vibrational amplitude calculation, however, supports the assignment for the axial bending frequency occurring higher than the in-plane bending frequency.