Photoionization of HOF with mass analysis

The ionization yields of HOF⁺, O⁺, and OH⁺ have been studied as a function of wavelength in the photoionization of HOF. The first ionization potential of HOF is 12.71±0.01 eV. The threshold for O⁺ formation, 14.34 eV, leads to ${\mathrm{\Delta \; H}}_{\text{f0}}^0\mathrm{\hspace{0.17em}(}\mathrm{HOF}\text{)=−22.8± 1\hspace{0.17em}}\mathrm{kcal/mole}$ . The threshold for OH⁺ formation, 15.07 eV, leads to a value for ${\mathrm{\Delta \; H}}_f^0\mathrm{\hspace{0.17em}(}\mathrm{HOF})$ in good agreement with the above result if one of two discrepant values for ${\mathrm{\Delta \; H}}_f^0\mathrm{\hspace{0.17em}(}{\mathrm{HO}}^{+})$ is chosen. This choice implies that the ionization potential for OH is 12.9_o±0.05 eV. The proton affinity of OF is 5.8₂ eV. Pronounced structure in the ionization yield curves is interpreted as vibrational autoionization in the region near threshold, and as electronic autoionization at higher photon energies.