Thermodynamics of gaseous zirconium and hafnium fluorides

An MS 1301 magnetic mass spectrometer has been used over a wide temperature range to examine vapor-state equilibria involving zirconium and hafnium fluorides. The enthalpies of formation have been determined for all the lower fluorides of those elements. These results are new for zirconium and hafnium monofluorides and also for hafnium difluoride and trifluoride. The recommended values are $\Delta_fH^0(\mathrm{HfF}_3, g, 0) = -1075 \pm 13, \Delta_fH^0(\mathrm{ZrF}_3, g, 0) = -1078 \pm 15, \Delta_fH^0(\mathrm{HfF}_2, g, 0) = -512 \pm 12, \Delta_fH^0(\mathrm{ZrF}_2, g, 0) = -483 \pm 16, \Delta_fH^0(\mathrm{HfF}, g, 0) = 53 \pm 12, \Delta_fH^0(\mathrm{ZrF}, g, 0) = 63 \pm 12$ kJ $\cdot$ mole$^{-1}$. The measurements have been used to calculate the equilibrium vapor compositions and the bond energies. The recommended values are $D^0(0), n$: $D^0(\mathrm{ZrF}_3$–$\mathrm{F}) = 665 \pm 15, D^0(\mathrm{ZrF}_2$–$\mathrm{F}) = 672 \pm 18, D^0(\mathrm{ZrF}$–$\mathrm{F}) = 623 \pm 16, D^0(\mathrm{Zr}$–$\mathrm{F}) = 612 \pm 15, D^0(\mathrm{HfF}_3$–$\mathrm{F}) = 702 \pm 18, D^0(\mathrm{HfF}_2$–$\mathrm{F}) = 640 \pm 20, D^0(\mathrm{HfF}$–$\mathrm{F}) = 642 \pm 14, D^0(\mathrm{Hf}$–$\mathrm{F}) = 646 \pm 15$, kJ $\cdot$ mole$^{-1}$.