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Coincidence ion pair production (I + + I − ) (cipp) spectra of I 2 were recorded in a double imaging coincidence experiment in the one-photon excitation region of 71 600–74 000 cm −1 . The I + + I − coincidence signal shows vibrational band head structure corresponding to iodine molecule Rydberg states crossing over to ion-pair (I + I − ) potential curves above the dissociation limit. The band origin ( ν 0 ), vibrational wavenumber ( ω e ) and anharmonicity constants ( ω e x e ) were determined for the identified Rydberg states. The analysis revealed a number of previously unidentified states and a reassignment of others following a discrepancy in previous assignments. Since the ion pair production threshold is well established, the electric field-dependent spectral intensities were used to derive the cutoff energy in the transitions to the rotational levels of the 7pσ(1/2) ( v ′ = 3) state. 

Coincidence ion pair production (cipp) spectra of F 2 were recorded on the DELICIOUS III coincidence spectrometer in the one-photon excitation region of 125 975–126 210 cm −1 . The F + + F − signal shows a rotational band head structure, corresponding to F 2 Rydberg states crossing over to the ion pair production surface. Spectral simulation and quantum defect analysis allowed the characterization of five new molecular Rydberg states (F 2 **): one Π and four Σ states. The lowest-energy Rydberg state spectrum observed ( T 0 = 125 999 cm −1 ) lacked some of the predicted rotational structure, which allowed an accurate determination of the ion pair production threshold of 15.6229 4 ± 0.0004 3 eV. Using the well-known atomic fluorine ionization energy and electron affinity, this number leads to a ground state F–F dissociation energy of 1.6012 9 ± 0.0004 4 eV. Photoelectron photoion coincidence (PEPICO) experiments were also carried out on F 2 and the dissociative photoionization threshold to F + + F was determined as 19.0242 ± 0.0006 eV. Using the atomic fluorine ionization energy, this can be converted to an F 2 dissociation energy of 1.6013 2 ± 0.0006 2 eV, further confirming the cipp-derived value above. Because the two experiments were independently energy-calibrated, they can be averaged to 1.6013 0 ± 0.0003 6 eV and this value can be used to derive the fluorine atom's 0 K heat of formation as 77.25 1 ± 0.01 7 kJ mol −1 . This latter is in excellent agreement with the latest Active Thermochemical Table (ATcT) value but improves its accuracy by almost a factor of three. 

The dissociative photoionization of 1,3‐dioxolane was studied by photoelectron photoion coincidence (PEPICO) spectroscopy in the photon energy range of 9.5–13.5 eV. Our statistical thermodynamics model shows that a total of six dissociation channels are involved in the formation of three fragment ions, namely, C₃H₅O₂⁺(m/z73), C₂H₅O⁺(m/z45), and C₂H₄O⁺(m/z44), with two channels contributing to the formation of each. By comparing the results of ab initio quantum chemical calculations to the experimentally derived appearance energies of the fragment ions, the most likely mechanisms for these unimolecular dissociation reactions are proposed, including a description of the relevant parts of the potential energy surface.