Energetics and rearrangements of the isomeric picoline dications

The second ionization energy of β-picoline was determined from photoionization experiments as 2IEβ = (24.05 ± 0.1) eV and the threshold for the dehydrogenation of the dication generated by photoionization as AE(–H2)β = (25.0 ± 0.2) eV. The second ionization energy is about 0.5 eV lower than values recently determined for α- and γ-picoline, whereas the energies required for dehydrogenation are similar. In order to rationalize the different behavior of dications generated from these isomeric picolines, we have performed a mass spectrometric investigation of the fragmentation patterns of the individual picoline dications and an extensive series of DFT calculations to explain the observed spectra.

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► The double ionization threshold (2IE) for β-picoline is 24.05 ± 0.1 eV.
► 2IE of β-picoline is about 0.5 eV lower than 2IE of α- and γ-picolines.
► β-picoline dication is generated preferentially in the singlet ground state.
► α- and γ-picolines are generated as mixtures of singlet and triplet states.