Kinetic Energy of Ions Produced by Photoionization of HF and F2

Kinetic energies were measured for the positive ions produced in the ion‐pair formation processes $$\mathrm{HF}\mathrm{+h\Lambda \to }{\mathrm{H}}^{+}+{\mathrm{F}}^{-},$$ $${\mathrm{F}}_2\mathrm{+h\Lambda \to }{\mathrm{F}}^{+}+{\mathrm{F}}^{-}$$ at a number of wavelengths in the region of the thresholds for these processes. The measurements prove that $D_0\mathrm{(HF)}$ is either 5.91 ± 0.02 or 5.87 ± 0.02 eV, depending on the value of the electron affinity of the F atom. Since the latter value for $D_0\mathrm{(HF)}$ is in good agreement with other more precise determinations, these results support the value E.A.(F) = 3.400 eV. The kinetic energy measurements also prove that $D_0({\mathrm{F}}_2\text{)\hspace{0.17em}=\hspace{0.17em}1.58\hspace{0.17em}±\hspace{0.17em}0.03}\mathrm{eV}$ . The measurements strongly suggest that the F⁺ ions from F₂ are produced not only in the ${}^3{P}_2$ ground state but also in ${}^3{P}_1$ and/or ${}^3{P}_0$ states as well. At higher photon energies, the F⁺ ions from F₂ are also produced in the ${}^{1}D$ state. Dissociation and predissociation processes of the molecular ions are discussed.