To lower E0, the key idea was to add a second aryl group to benzylpyridiniums to weaken the C-N bond (Figure ) . Quantum chemical calculations at the DLPNO-CCSD(T)/CBS//PBE0-D3BJ level give E0 between 0.70 and 1.74 eV (Table ). The calculated value were confirmed by GIBMS. The dissociation energy is lower because the fragment is more stable than the classical R-BnPy + . The study also provides appearance energies, considering the kinetic shift at different time scales. Table . Calculated (DLPNO-CCSD(T)/CBS//PBE0-D3BJ) and experimental (guided ion beam mass spectrometry, GIBMS) dissociation energies E0 for the pyridine loss of benzhydrylpyridinium ions . Appearance energies are given for a time constant of 10 -4 s; values for values at  = 2 × 10 -4 s and 5 × 10 -4 , see Tables and of . In 2017, the Kappes group introduced benzylpyridinium-substituted porphyrins (cationized or not) as higher-mass, multiply charged thermometer ions . The H2P 4+ derivative (Figure ) has 384 degrees of freedom. They fragment by the successive losses of pyridine molecules. The bond dissociation energies calculated using the BP86 functional and def-SVP basis set range between 1.30 eV (HP 3+ , first pyridine loss) to 3.11 eV (H2P 4+ , third pyridine loss). The molecules were used to evaluate bond dissociation energies in a linear ion trap, but to date, they were not used to evaluate internal energies in ionization sources.