Photoionization Mass Spectrometric Study of F₂, HF, and DF

From an analysis of the threshold region for formation of F2+ by photoionization of F2, the value 15.686 ± 0.006 eV has been deduced as the first ionization potential. The process F2+hν→F++F− begins at slightly lower energy and is traced to Landau–Zener-type crossing from certain Rydberg states to a potential curve leading to the separated ions in their ground states. The Rydberg states are those converging to the ground state of F2+, Π2. The ion-pair process is still significant at higher energy, in the vicinity of the threshold for the process F2+hν→F++F+e. Subtracting the intensity of F− from that of F+ in this energy region yields a corrected threshold of 19.01 eV, which gives D0(F2) = 1.59 ± 0.01 eV. The photoionization of HF (and DF) also gives rise to these three prominent processes, i.e., parent ionization, pair formation, and dissociative ionization. The ionization potential is found to be 16.007 ± 0.01 eV for HF (16.030 ± 0.01 eV for DF). The corrected threshold for H+ is 19.445 eV (19.513 eV for D+) which gives D0(HF) = 5.845 ± 0.01 eV. Quantitative descriptions are given for the autoionization peaks observed in both the F2 and HF spectra.