The Vagabond Fluorine Atom: Dissociative Photoionization of trans-1,3,3,3-Tetrafluoropropene

The dissociative photoionization of trans-1,3,3,3-tetrafluoropropene (HFO-1234ze) was investigated by imaging photoelectron photoion coincidence (PEPICO) spectroscopy. From the threshold photoelectron spectrum (TPES), an adiabatic ionization energy of 10.91 ± 0.05 eV is determined and reported for the first time. Over a 4 eV wide range, internal-energy selected trans-1,3,3,3-tetrafluoropropene cations decay by three parallel dissociative photoionization channels, which were modeled using statistical theory. The 0 K appearance energies of CF₂CHCF₂ (H-loss, m/z 113), CFHCHCF₂ (F-loss, m/z 95), and CH₂═CF₂ (CF₂-loss, m/z 64) fragment ions were determined to be 12.247 ± 0.030, 12.66 ± 0.10, and 12.80 ± 0.05 eV, respectively. From the last, the heat of formation of neutral trans-1,3,3,3-tetrafluoropropene was determined to be -779.9 ± 9.7 kJ/mol. While the lowest-energy fluorine loss occurs directly, the first H-loss and CF₂-loss channels involve both a fluorine- and a hydrogen-migration prior to dissociation. At higher internal energies, several other rearrangement pathways open up, which involve fluorine and hydrogen transfer and, through fluorine loss, lead to the formation of several additional isomeric allylic fragment ions.